Set your oven to bake at 450β and prepare your vegetable for roasting by slicing the red peppers into quarters, and the portobello mushrooms and zucchini into ΒΌ inch slices. Brush the veggies lightly with cooking oil and season with salt and pepper.
Roast the vegetables for 20 mins. When the vegetables have finished roasting, set the oven to broil.
Build your sandwiches by placing arugula on the bottom half of the bun, and top with the roasted zucchini, mushrooms and red pepper. Finish with a couple of slices of brie cheese.
Place the sandwiches (without the top half of the bun) under the broiler for just about 30 seconds to begin melting the brie.
Spread the top half of the bun with pesto, and place on the sandwich then serve.