In baking dish, place chicken with olive oil, garlic & any herbs and spices you like (basil, parsley, oregano, etc) & some himalayan salt to taste. Bake at 425 degrees, about 20 minutes or just pink in the center. In the meantime, saute the spinach and prepare sauce (diced tomatoes, tomato sauce, butter, balsamic vinegar); once it is bubbling, lower heat to simmer about 10 minutes. Then place sauce & spinach in the pan with the chicken. Cook an additional 10 minutes. Finally, sprinkle feta in pan & broil until sauce is bubbly and feta is slightly melted & starting to brown.