Preheat your oven to 400°F (200°C). Dice your chosen vegetables, spread them out on a baking sheet, drizzle with olive oil, and sprinkle with salt and pepper. Roast for about 15-20 minutes.

While the vegetables are roasting, take two slices of crusty whole grain bread. Spread mayonnaise on one side of each slice, add a slice of cheese on the unspread side, layer with roasted vegetables, and top with another slice of cheese before closing the sandwich.

Place a skillet over medium heat and warm it. Carefully place the sandwich in the skillet, mayonnaise side down, and cook for approximately 3-4 minutes, until golden brown.

After 3-4 minutes, flip the sandwich and spread mayonnaise on the top side. Cook for an additional 3-4 minutes until both sides are crispy and the cheese melts inside.

Once cooked, remove the sandwich from the skillet, let it cool for a minute before slicing in half, and serve with fries or salad.