1 small head broccoli, cut into small florets
1 tbsp. olive oil
Kosher salt and black pepper
4 portobello mushrooms (stems removed), sliced ½-inch thick
2 red bell peppers, seeded and sliced ½-inch thick
¼ cup light mayonnaise
1 clove garlic, minced or pressed
4 thick slices country bread
2-4 oz. provolone cheese, thinly sliced
Preheat a broiler with a rack placed 4 inches from the heat source. Line a rimmed baking sheet with aluminum foil. Place the broccoli on the baking sheet, drizzle with the olive oil and season with salt and pepper. Toss to combine. Broil until the broccoli begins to brown, tossing once or twice, about 4-6 minutes.
Add the sliced mushrooms and peppers to the pan with the broccoli and toss to combine. Broil, tossing once or twice, until the vegetables are tender, 8-10 minutes more. Set aside.
Meanwhile, combine the mayonnaise and garlic in a small bowl; season with salt and pepper. Place the slices of bread on a work surface. Spread each slice of bread with 1 tablespoon of the garlic-mayo mixture. Top with the cooked vegetables, then the cheese. Line the baking sheet with a new piece of foil. Transfer the assembled sandwiches to the baking sheet. Broil until the cheese is melted and lightly browned, 2-4 minutes.