Preheat the panini oven to 350°F (180°C). Cut the bell pepper into 8 pieces and remove the seeds. In a bowl, toss with garlic, olive oil, salt, and pepper.
Cook the peppers: Place them in the panini oven, close, and cook for 7 to 10 minutes. Once cooked, return them to the bowl and add the balsamic vinegar and basil. Let cool. Wipe the oven plates with a paper towel or damp cloth.
Assemble the sandwiches: Lay 4 slices of bread on a work surface and spread with marinara sauce. Distribute the grilled peppers, tomato slices, and mozzarella. Season generously, then add arugula and antipasto to taste. Top with the remaining bread slices.
Cook: Preheat the panini oven to 375°F (190°C). Place the sandwiches inside, close, and cook for about 3 minutes, or until the bread is golden brown.
Serve: Remove from the oven, cut in half, and enjoy.
