2 (6 oz.) cans tuna
4 oz. can mushrooms, sliced & drained
1 tbsp. grated onion
1 c. mayonnaise
1/2 c. cheddar cheese, shredded
1 1/2 c. celery, diced
1/2 c. ripe olives
1 tsp. lemon juice
2 c. Corn Chex
1 tbsp. butter

Preheat oven to 350 degrees. Combine everything but Corn Chex and cheese. Stir in Chex. Spoon into casserole. Bake 15 minutes. Spread cheese over top. Crush 1 cup of the Corn Chex, sprinkle over cheese. Return to oven and bake another 10 to 15 minutes.