Heat olive oil in a large stockpot over medium-high heat.
Add diced chicken breast and cook until browned on all sides, approximately 5-7 minutes.
Add onion, carrots, and celery to the pot and sauté until vegetables are softened, about 6 minutes.
Stir in minced garlic, cumin, and smoked paprika; cook for 60 seconds until fragrant.
Add rinsed lentils, chicken bone broth, and diced tomatoes with their juices.
Bring the mixture to a boil, then reduce heat to low, cover, and simmer for 25 to 30 minutes or until lentils are tender.
Stir in the fresh spinach and cook for 2 minutes until wilted.
Remove from heat, stir in lemon juice, salt, and pepper, then serve warm.