Hamburger
Cook up some burger, season it with salt, pepper, maybe some chili powder, and mix it in.
Chicken
Buy a roasted chicken, tear it up, and put it in there. You can also try spicing up the chicken with some seasoning and olive oil or butter. Try salt, pepper, oregano, chili powder.
Sausage
Cook your favorite sausage, such as breakfast, chicken, or Italian, and add it into the dish.
Mushrooms
Buy some sliced mushrooms, sauté them in butter or olive oil, add some salt and pepper, throw them on top.
Green Peppers
Cut up a green pepper, sauté it in butter or olive oil, add salt and pepper, and mix it in.