Recipe

Rainbow Lentil Soup

A healthy, wholesome slow cooker soup with red lentils, sweet potato, kale, and a bright lemon herb finish. Cozy, weeknight easy, and big on flavor.

By Matt Campbell

•

4.8

A bowl of hearty lentil soup with kale and sweet potato, topped with a swirl of yogurt and chopped herbs on a wooden table with a spoon nearby

Jump to Recipe

Some slow cooker soups taste like they were made by a committee. This one tastes like you actually meant to cook today. It is warm and wholesome, yes, but it also has personality: creamy red lentils, sweet chunks of sweet potato, a little tomato depth, and a lemony herb finish that wakes the whole bowl up.

It is the kind of slow cooker recipe you can start on a busy morning, forget about for hours, and still get that okay wow moment when you taste and adjust at the end. Minimal drama. Maximum cozy.

Ingredients for lentil soup on a kitchen counter, including lentils, chopped carrots, celery, onion, sweet potato, garlic, and a lemon

Why It Works

Big flavor without heavy ingredients: Red lentils break down into a naturally creamy base, so you get richness without cream.
Healthy, but not boring: Smoked paprika, cumin, and a lemon finish make it taste bold and bright, not flat.
Flexible and forgiving: Use what you have for veggies and greens. This soup welcomes substitutions.
Meal prep friendly: It holds up beautifully for lunches and freezes like a champ.

Pairs Well With

Storage Tips

Refrigerate: Cool completely, then store in airtight containers for up to 5 days. The soup will thicken as it sits. That is normal and honestly kind of great.

Reheat: Warm on the stove over medium-low or microwave in 60 to 90 second bursts. Add a splash of broth or water to loosen to your preferred texture. Finish with a fresh squeeze of lemon if it tastes muted.

Freeze: Freeze in freezer-safe containers for up to 3 months. Thaw overnight in the fridge or gently on the stove. Stir well to bring it back together.

Common Questions

Can I use green or brown lentils instead of red?

You can, but the texture changes. Green or brown lentils hold their shape and usually take longer. If you swap them in, plan on 6 to 8 hours on LOW (or until tender). For a creamier vibe, blend a portion at the end.

Is this soup spicy?

Not as written. The smoked paprika is more smoky than hot. If you want heat, add 1/4 to 1/2 teaspoon crushed red pepper flakes or a diced jalapeño.

How do I make it vegan?

It is already vegan if you use vegetable broth and skip the yogurt swirl and parmesan. For a creamy topping, try unsweetened coconut yogurt or a cashew cream drizzle.

My soup tastes bland. What should I do?

Three fast fixes: add salt in small pinches, squeeze in more lemon, and stir in something savory like 1 teaspoon miso or a little extra tomato paste. Taste as you go. You are the boss.

Can I cook it on HIGH?

Yes. Cook on HIGH for 3 to 4 hours. Add the kale at the end so it stays bright and not overcooked.

Matt Campbell

I have always had a huge passion for the culinary arts, people, working as a team, and so on. I wanted to pursue my love for cooking initially at Virginia Commonwealth University with a culinary arts degree; however, I instead decided to apply myself and acquire more practical skills. My end goal is to eventually open my own restaurant or similar establishment.

Kitchen Essentials

6-quart slow cooker
Cutting board and sharp knife
Measuring cups and spoons
Wooden spoon or ladle
Immersion blender (optional, for extra creamy texture)
Citrus juicer or reamer (optional, but nice)

I love the idea of culinary school, but what really taught me to cook was repetition and real life: hungry people, limited time, and a stubborn desire to make something that tastes like more than the effort it took. This soup is one of my favorite examples. It started as a clean out the fridge slow cooker situation and turned into a regular because it hits every note I want in a bowl: cozy carbs, bright finish, and enough seasoning to make you stop mid-bite and recalibrate your day.

Rainbow Lentil Soup

(4.8 Reviews)

Prep Time 25 minutes

Cook Time 6 hours

Total Time 6 hours 25 minutes

Servings 6

Ingredients

1 tablespoon olive oil
1 large yellow onion, diced
3 carrots, diced
2 celery stalks, diced
4 cloves garlic, minced
1 tablespoon tomato paste
1 1/2 cups red lentils, rinsed and picked over
1 medium sweet potato, peeled and diced (about 2 cups)
1 (14.5-ounce) can diced tomatoes
6 cups low-sodium vegetable broth (or chicken broth)
1 teaspoon ground cumin
1 teaspoon smoked paprika
1/2 teaspoon dried thyme
1 bay leaf
1 teaspoon kosher salt, plus more to taste
1/2 teaspoon black pepper
3 cups chopped kale (stems removed) or baby spinach
1 lemon, zested and juiced
2 tablespoons chopped fresh parsley or cilantro
Optional toppings: plain Greek yogurt, toasted pumpkin seeds, extra olive oil, grated parmesan

Instructions

Build the base. Add olive oil, onion, carrots, celery, garlic, tomato paste, lentils, sweet potato, diced tomatoes, broth, cumin, smoked paprika, thyme, bay leaf, salt, and pepper to the slow cooker. Stir well.
Cook. Cover and cook on LOW for 6 hours (or HIGH for 3 to 4 hours) until the sweet potato is tender and the lentils are very soft.
Make it creamy, your way. Remove the bay leaf. For a thicker, creamier soup, use an immersion blender to blend 10 to 20 seconds. Keep it a little chunky for texture. Note: Red lentils break down a lot over a full 6 hours, so the soup can get thick. Add a splash of broth or water if you want it looser.
Add greens at the end. Stir in kale. Cover and cook on HIGH for 5 to 10 minutes, just until wilted and tender. (If using spinach, 2 to 5 minutes is plenty.)
Finish bright. Stir in lemon zest, lemon juice, and fresh herbs. Taste and adjust with more salt, pepper, or lemon.
Serve. Ladle into bowls and top with yogurt, seeds, or a drizzle of olive oil if you want that extra restaurant soup energy.

Nutrition information is estimated.

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