Combine ground beef with chopped onion and salt. Form into balls the size of walnuts. Brown on all sides in hot skillet. Stir in catsup, brown sugar, vinegar and mustard; bring to boil. In greased 2 quart casserole, combine beans and pineapple chunks. Arrange meat balls on top; pour sauce over all. Bake in 350F oven for 30-40 minutes. Makes 6-8 servings.