Preheat the oven to 450°F.
In a food processor, combine peas, basil, parmesan cheese, pine nuts, garlic, olive oil, lemon zest and juice , salt, pepper, and red pepper flakes, if preferred.
Process in short bursts until everything is well combined, about 30 seconds.
Spread the pesto on the flatbread.
Top with thinly sliced mozzarella cheese and sliced tomatoes.
Bake for 7-10 minutes, or until the edges of the flatbread are slightly browned.