Maple Tuna Olive Toastie

Heat butter in a small frying pan over medium heat, and cook and stir onion for 3 minutes. Reduce heat to medium-low, stir in maple syrup, and cook until onions are soft and golden, 7 to 10 minutes.

Set oven rack about 8 inches from the heat source and preheat the oven's broiler.

Stir together tuna and salad dressing in a bowl; season with salt and pepper. Slice bread loaf in half horizontally, then halve both pieces lengthwise, making four equal pieces. Place bread, crust-side down, on a baking sheet. Layer tuna mixture, onion, and Cheddar cheese evenly over bread pieces.

Broil in the preheated oven until cheese is bubbly, about 5 minutes.