Start by prepping your ingredients: dice the carrots, celery, and onion into small, uniform pieces for even cooking. Rinse the lentils thoroughly in cold water until the water runs clear to remove any dust.
In a skillet over medium heat, toast the curry powder and turmeric in a splash of oil until fragrant—about 1-2 minutes—this deepens their flavor and brings out their aromatic oils.
Add the toasted spices to the slow cooker along with the chicken thighs, diced vegetables, rinsed lentils, coconut milk, and chicken broth. Stir everything together so the spices evenly coat the ingredients.
Set your slow cooker to low and cook for 6 to 8 hours. During the first hour, occasionally lift the lid to check the aroma—your house will fill with spicy, coconut-scented warmth.
After 6 hours, check that the lentils are soft and breaking down, and the chicken is tender enough to shred easily. If needed, add a splash more broth and continue cooking until everything is nicely melded.
Stir in fresh lemon juice to brighten the flavors, then taste and adjust salt or spice if desired. If you prefer a thicker, creamier soup, cook uncovered for an additional 10 minutes.
Serve the Mulligatawny hot, ladled into bowls, garnished with chopped cilantro or a dollop of yogurt if you like. Pair with crusty bread or rice for a complete, satisfying meal.
