Place the muffin halves, cut side up, on a foil-lined baking sheet.
Broil about 6 inches from heat for 2 to 3 minutes, or until toasted.
In a bowl, combine the tuna, onions, bell pepper, egg, mayonnaise, and mustard. Spread the tuna mixture over the English muffin halves and top with the cheese srips, criss-cross fashion.
Broil about 6 inches from heat for about 3 minutes, or until cheese is melted.
Calories per serving: 378