1Heat oven to 350°. Mix tuna, celery, onion, lemon peel and mayonnaise in medium bowl.
2Spread about 3 tablespoons tuna mixture on each English muffin half. Top each with tomato slice; sprinkle with cheese. Place on ungreased cookie sheet.
3Bake 8 to 10 minutes or until cheese is melted and sandwiches are thoroughly heated.