Toast the bagel halves lightly before spreading to add texture and prevent sogginess. For best results, use fresh pesto and a good quality Parmesan cheese. When heating, watch closely as toaster ovens can brown quickly; you want the cheese melted and slightly bubbly. A quick broil at the end can give the cheese a nice golden finish. Consider adding a sprinkle of red pepper flakes for a touch of heat or a drizzle of balsamic glaze after heating for extra flavor.