1. Preheat the oven to 200°F (95°C). Drizzle the bread on both sides with the oil.

2. Top four bread slices with the mozzarella, tomatoes, and basil. Season with salt and pepper.

3. Top with the remaining bread and compress with your hands, making sure none of the filling is sticking out.

4. Heat a heavy frying pan over high heat. Add 1 tbsp oil and tilt to coat the bottom of the pan. Carefully add 2 sandwiches. Cook, turning once, about 5 minutes, until golden on both sides. Transfer to a baking sheet and keep warm while frying the remaining sandwiches in the remaining 1 tbsp oil.

5. Toss the arugula with the vinegar in a medium bowl. Slice each sandwich in half and transfer each to a plate. Add equal amounts of the salad, and serve immediately.