Cut the chicken breast into bite-sized chunks and season generously with salt and freshly ground black pepper—this ensures the chicken is flavorful throughout, not just on the surface. Dice the onion, carrots, and celery into 1/2-inch pieces for even cooking and a pleasant texture in the finished soup. Mince the garlic fresh and set aside. Measure out the lentils, broth, tomatoes, and all dry seasonings. Having everything prepped and ready makes the actual cooking process smooth and prevents overcooking any components while you're still chopping.

Heat the olive oil in a large pot over medium heat until shimmering. Add the diced onion, carrots, and celery together and cook for 6 minutes, stirring occasionally, until they begin to soften and the onion becomes translucent. This creates a flavorful foundation and allows the vegetables to release their natural sweetness. Add the minced garlic, salt, smoked paprika, and cumin, then cook for 1 minute more, stirring constantly—this brief cooking time blooms the spices and distributes their flavors evenly throughout the aromatic base without burning the garlic.

Add the seasoned chicken chunks, green lentils, fire-roasted diced tomatoes with their juice, and chicken broth to the pot. Stir well to combine and bring the mixture to a boil over medium-high heat. Once boiling, reduce the heat to medium-low and simmer for 25 minutes, stirring occasionally. The lentils will soften and become tender while the chicken cooks through completely. I find that simmering gently rather than boiling vigorously keeps the broth clear and prevents the lentils from breaking apart too much, giving you a soup with better texture and visual appeal.

Add the fresh spinach to the pot and stir continuously for 1–2 minutes until it completely wilts into the soup. Taste the soup and adjust the seasoning with additional salt and freshly ground black pepper as needed. The spinach adds a bright, nutritious finish and a subtle earthiness that complements the lentils and chicken beautifully. I always add the spinach at the very end to preserve its fresh flavor and vibrant color—if it simmers too long, it loses both.