Start by gathering your equipment: a slow cooker, a skillet, a knife, and a cutting board. Prepare your ingredients by dicing the chicken thighs into bite-sized pieces and rinsing the lentils thoroughly.
In a dry skillet over medium heat, toast the cumin seeds, coriander seeds, and turmeric for 1-2 minutes until fragrant, stirring constantly. Transfer the toasted spices to a small bowl.
In the same skillet, add a tablespoon of oil and sauté the diced onion and minced garlic until the onion becomes translucent and fragrant, about 5 minutes.
Add the toasted spices to the skillet and stir for 30 seconds to release their aroma, then transfer the mixture into the slow cooker.
Place the chicken, diced carrots, chopped celery, and rinsed lentils into the slow cooker. Pour in the chicken broth and coconut milk, then stir everything together to combine.
Cover and set the slow cooker to low. Let it cook for 6 to 8 hours, until the lentils are soft and the chicken is tender and falling apart.
Halfway through cooking, check the soup’s consistency. If it looks too thick, stir in a splash of broth. Ensure everything is simmering gently and ingredients are submerged.
Near the end of cooking, stir in the freshly squeezed lemon juice and season with salt and pepper to taste. Taste and adjust the acidity or seasoning as needed.
Once the chicken is tender and the soup has thickened slightly, turn off the heat and let it sit uncovered for 5 minutes, allowing flavors to settle.
Ladle the Mulligatawny into bowls, garnishing with chopped cilantro and lime wedges. Serve hot, enjoying the fragrant, creamy soup with a bright and spicy kick.
