Cook the pasta shells according to package instructions until al dente. Drain and set aside to cool slightly.
In a mixing bowl, combine the ricotta cheese, half of the mozzarella cheese, Parmesan cheese, basil pesto, beaten egg, garlic powder, salt, and pepper. Mix until well combined.
Using a spoon, carefully fill each pasta shell with the ricotta mixture and place them in a greased baking dish.
Spread the marinara sauce evenly over the stuffed shells.
Sprinkle the remaining mozzarella cheese on top of the sauce-covered shells, and add a few dollops of extra basil pesto for added flavor.
Cover the baking dish with aluminum foil and bake for 20 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and lightly golden.
Remove from the oven and let it cool for a few minutes before serving.
Garnish with fresh basil leaves.
Notes
Let the dish cool slightly before serving for better flavor.