How to Make a Tuna Melt

Name: How to Make a Tuna Melt
Prep time: 15 min
Cook time: 10 min
Total time: 25 min
Cuisine: American
Ingredients: 1 (6.5 ounce) jar oil-packed tuna, drained; 2 tablespoons finely diced celery; 1 tablespoon minced green onion; 2 teaspoons capers, drained; 2 tablespoons mayonnaise, or more to taste; 1 teaspoon Asian chile paste (such as sambal oelek); 0.33333334326744 cup fresh mozzarella cheese; salt and ground black pepper to taste; 2 tablespoons softened butter, divided; 2 thick slices French bread; 0.25 cup shredded sharp white Cheddar cheese, divided; 1 pinch cayenne pepper, or to taste