Preheat oven to 375 degrees. Heat olive oil in skillet and addbeef and onion. Cook. Put meat and onion in bowl and mix with bread crumbs, cheese, eggs, spinach, salt and pepper. Stuff manicotti with mix and put in 11 3/4x7 1/2x1 3/4" dish. Spoon tomato on top, cover with foil, and bake 45 min.