Put the lentils in a wire strainer and rinse with cool water. Combine the lentils, rice, mushrooms, celery, onions, bouillon granules, garlic, Italian seasoning, black pepper, and water in a 4-quart pot, and bring to boil over high heat.
Reduce the heat to low, cover, and simmer for 40 minutes.
Add the undrained tomatoes and cook for an additional 20 minutes or until the lentils are soft and the liquid is thick.
Add the spinach and olive oil and cook for another minute or two or until the spinach is wilted. Serve hot, topping each serving with some of the parmesan cheese if desired.