Shrimp-Rice Casserole

1 finely chopped onion
1/2 green bell pepper, finely chopped
1 stalk celery, finely chopped
3 cups cooked rice
1 can cream of mushroom soup
1/2 can milk
1 (12 ounce) package frozen shrimp,
    cooked and finely chopped

Saut? onion, bell pepper and celery in a small amount of oil. Remove from heat, then add rice, mushroom soup which has been diluted with milk, and shrimp, cooked and finely chopped. Please mixture in a buttered casserole dish. Sprinkle 1/2 cup grated Cheddar cheese over the top and bake, uncovered, at 300 degrees F for one hour.