Preheat the oven's broiler and set the oven rack about 6 inches from the heat source.
Mix the mayonnaise, Cheddar cheese, green onions, salt, garlic salt, and pepper in a bowl. Spread the cheese mixture over each English muffin half. Cut the muffins into quarters and place on a baking sheet.
Broil in the preheated oven until cheese is bubbly, 4 to 6 minutes.