1 lb. ground beef
1 med. onion, chopped
1 tsp. oregano
1/4 c. oil
2 pkgs. chopped spinach, thawed and drained
1 (7 oz.) can mushrooms, drained
1 can cream of celery soup
1 c. sour cream or yogurt
7 lg. slices Mozzarella cheese

Brown beef, onion, and oregano in oil. Add spinach, soup, sour cream, and mushrooms. Pour into a 9 x 13 dish. Place Mozzarella on top and bake uncovered 30 minutes at 350 degrees.