Step 1

Heat broiler, with rack in highest position. In a medium bowl, combine tuna, mayonnaise, onion, capers, lemon juice, salt, pepper, dill, garlic powder and mix until well combined.

Step 2

Arrange bread on a baking sheet and spread 1/2 Tablespoon on each slice. Divide tuna salad evenly among slices, then top each with 2 slices tomato and 2 slice cheese, overlapping. Broil until cheese is melted and bubbling, 3 to 4 minutes.