Preheat oven to 425°F with a baking sheet inside to heat up.
Season sliced chicken with olive oil, garlic powder, Italian seasoning, salt, and pepper. Cook in a skillet over medium-high heat for 3 to 4 minutes per side. Rest and slice thin.
Spread pesto evenly over each flatbread. Arrange mozzarella slices across the surface.
Bake on the hot pan for 8 to 10 minutes until cheese is melted and edges are golden.
Top with sliced chicken, cherry tomatoes, and fresh basil leaves immediately after removing from the oven.
Drizzle with balsamic glaze, add flaky salt if using, slice, and serve immediately.