Grill the vegetables: Start by heating olive oil in a grill pan or skillet over medium heat. Add the sliced zucchini, red bell pepper, and red onion. Sprinkle with Italian herbs, salt, and pepper. Grill for 5–7 minutes, turning occasionally, until the vegetables are tender and lightly charred. Drizzle the balsamic vinaigrette over the warm veggies and toss gently to coat.

Prepare the bread: If you like a golden crust, spread a thin layer of mayonnaise on the outside of each slice of bread. This helps with crispiness and adds a hint of richness (you can use butter if preferred).

Assemble the sandwich: On two slices of bread, layer the provolone cheese, followed by the grilled, vinaigrette-tossed vegetables. Add the second slice of cheese on top of the veggies, then close the sandwich with the remaining slices of bread.

Grill the sandwich melt: Place the sandwiches in a skillet over medium heat. Cook for 3–4 minutes on each side, pressing down gently with a spatula, until the bread is golden brown and the cheese is fully melted. Don’t rush—low and slow gives the cheese time to melt beautifully without burning the bread.

Serve hot: Slice in half and serve immediately. The warm balsamic aroma, melted cheese, and crisp edges make this sandwich irresistible.