In a small mixing bowl, stir together cheese, mayonnaise or salad dressing, parsley, and mustard. Spread cheese mixture on 8 slices of the party rye. Top each with another slice of bread.
Arrange sandwiches in a ring on a microwave-safe plate. Cover with paper towel. Microcook on 50 percent power (medium) for 1 to 2 minutes or until the sandwiches are warm, turning the plate once. Makes 8 sandwiches.