Fry pork sausage, breaking up with fork, until meat is no longer pink, about 12 to 15 minutes. Pour off fat. While sausage is still warm, blend in cheese, oregano and catsup. Spread on rye bread.
Place on baking sheet and freeze. When frozen, pack in plastic bags or freezer container and freeze until ready to use.
To serve, place frozen appetizers on baking sheet. Heat in oven at 350° for about 8 minutes or until browned.
Makes 30 to 40 appetizers.
Note: If larger rye bread is used, cut slices in halves or quarters.