In a large pot, fry diced bacon until cooked. Remove bacon and drain, reserving 1 tablespoon of bacon grease in the pot. Add the onion and saute until softened, about 5 minutes. Add garlic and saute 1 minute longer.
Add bacon back into pot, diced tomatoes with all the juice, lentils, chicken stock and water. Bring to boil then reduce to simmer. Cover pot and simmer for 15-25 minutes or until lentils are soft and cooked through.
Add the spinach and stir until wilted. Season with salt and pepper to taste. Serve with croutons.