Preheat the oven to 475°F (245°C) and line a rimmed baking sheet with parchment paper.
Heat 1 tablespoon of olive oil in a medium nonstick skillet over medium-high heat; add the finely diced onion and minced garlic and cook 3 to 4 minutes until softened, stirring often to prevent burning. Remove from heat and let cool slightly.
In a large mixing bowl combine the ground chicken, beaten egg, milk, bread crumbs, 1/3 cup Parmesan, chopped parsley, Italian seasoning, salt, black pepper, and crushed red pepper flakes.
Add the cooked onion and garlic to the bowl and mix until evenly combined.
Divide the mixture into 4 equal portions and shape each into an oval patty on the prepared baking sheet. Drizzle the remaining 1 tablespoon of olive oil over the patties.
Bake the patties in the preheated oven for 13 to 15 minutes, until the chicken is cooked through.
While the patties bake, stir together the marinara sauce and tomato paste in a small bowl until blended.
Remove the patties from the oven and spoon the marinara mixture evenly over each patty. Sprinkle 2 tablespoons Parmesan and the shredded mozzarella directly on top of each patty.
Return the baking sheet to the oven and bake 4 to 5 minutes more, until the cheese is melted and bubbly.
Optionally sprinkle a little extra chopped parsley over the finished patties before serving.
