Heat broiler with rack set 4 inches from heat.

Cut broccoli into small florets; discard stalk.

Remove stems from mushrooms and discard. Slice mushrooms 1/2 inch thick.

Remove ribs and seeds from peppers and discard. Cut peppers into 1/2-inch thick slices.

Crush garlic through a press.

Thinly slice Gouda cheese (if not already sliced).

Line a rimmed baking sheet with aluminum foil.

Toss broccoli with oil, then season with 1/8 teaspoon salt and 1/8 teaspoon pepper. Add to baking sheet and broil 4-6 minutes, tossing once or twice until broccoli begins to char.

Add mushrooms and bell peppers to the broccoli; season with remaining salt and pepper and toss to combine. Broil 8-10 minutes more until vegetables are tender, stirring occasionally; set aside.

Meanwhile, combine mayonnaise and garlic in a small bowl.

Place bread on a work surface and cut into thin slices. Spread each slice with mayonnaise mixture; top with vegetables and then cheese. Place on baking sheet and broil 2-4 minutes until cheese is melted and lightly browned.

Slice melts in half for a snack or eat whole as a meal.