Combine the grape tomatoes and 1 teaspoon of the olive oil, tossing to coat. Place the tomatoes in a single layer on a rimmed baking pan. Bake in the preheated oven for 10 minutes or until softened. Reduce the oven temperature to 375°F.
Place the flatbreads on 2 baking sheets. Bake at 375°F for 5 minutes or until beginning to crisp. Spread 1 tablespoon pesto on each flatbread. Sprinkle each with 1/4 cup mozzarella cheese and 1/2 cup roasted tomatoes. Bake at 375°F for 8 minutes or until the cheese is melted and bubbly.
While the flatbreads bake, combine the arugula and remaining 2 teaspoons olive oil, tossing well. Top the flatbreads evenly with arugula. Sprinkle with the red chile flakes, if desired.