Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Add diced chicken breast and cook until golden on all sides, about 4-5 minutes, stirring occasionally. Transfer chicken to a plate and set aside.

In the same pot, add diced onion, carrots, and celery to the remaining oil and sauté for 3-4 minutes until softened. This aromatic base builds the flavor foundation for your entire fall soup experience.

Stir in minced garlic and cook for 30 seconds until fragrant, then add red lentils, chicken broth, diced tomatoes with juice, thyme, oregano, salt, pepper, and bay leaf. Return the cooked chicken to the pot and bring everything to a simmer.

Reduce heat to medium and let the creamy hearty chicken lentil soup simmer for 20-25 minutes until lentils are completely tender and beginning to break down naturally. Stir occasionally to prevent sticking on the bottom.

Pour in heavy cream and stir until fully incorporated and the broth turns pale golden. Add fresh spinach and stir until wilted, about 2 minutes.

Taste and adjust seasonings as needed, then remove bay leaf before serving. The soup will continue thickening slightly as it cools.