Beef and Spinach Casserole

1 pound ground beef
1 medium onion, chopped
1 teaspoon oregano
1/2 teaspoon vinegar
2 packages chopped spinach, thawed and drained
7 ounce can of mushrooms, drained
1 can cream of celery soup
1 cup sour cream
Jack cheese

Brown the beef, onion and mushrooms. Add spinach and oregano. Season with salt and pepper to taste. Mix in soup, sour cream and vinegar. Pour into casserole dish. Top with Jack cheese. Bake at 350 degrees 20 to 30 minutes.