Place the peppers and tomatoes in an air fryer and pour over 2 tsp of olive oil and season with salt and pepper. Toss to coat the peppers and tomatoes evenly. Cook at 175°C/350°F for 15 minutes, tossing half way through. (Alternatively roast in the oven for 25 minutes at 175°C/350°F or 165°C/330°F fan.)
Spread each side of bread with the remaining olive oil. Spread each piece of bread with 1 tablespoon of pesto.
Top 1 slice of bread with the mozzarella pieces and drizzle with the balsamic glaze. Top the second slice of bread with the peppers and tomato. Flip the bread over to make a sandwich.
Heat a sandwich grill and grill the sandwich for 4-7 minutes until golden and the cheese is melted. (Alternatively fry on a medium high heat in a frying pan. Fry for around 3 minutes on each side until golden. You can cover the pan with a lid for a few minutes to help the cheese melt). Enjoy straight away.