Use store-bought pesto if you're short on time. Add grilled zucchini, mushrooms, or eggplant for a heartier flatbread. Make it vegan by skipping the cheese or using a plant-based pesto. Store leftovers 2 to 3 days refrigerated and reheat in a toaster oven or skillet until crisp. Pesto keeps up to 5 days refrigerated, or freeze it in cubes.