1. Preheat oven to 350°. Set tomato halves cut side up in an oiled baking pan and spread about 1/2 tsp. pesto over each. Bake until tomato halves are browned on top and slightly shriveled, about 1 1/2 hours.
2. Spread pesto generously over 4 slices of bread. Top with turkey, hot tomatoes, mozzarella, arugula leaves, and remaining slices of bread. Serve with remaining pesto if you like.
Note: Nutritional analysis is per sandwich.
You can make the pesto up to 2 days ahead of time; chill airtight, then bring to room temperature before using. Any leftover pesto could be layered with goat cheese on crostini, tossed with pasta, or served with roast chicken or broiled fish.