Bring a large pot of salted water to a boil. Cook the jumbo shells according to package instructions until al dente. Drain and set aside to cool slightly.
In a mixing bowl, combine ricotta cheese, half of the mozzarella cheese, chopped sun-dried tomatoes, grated Parmesan cheese, egg, minced garlic, dried basil, dried oregano, and red pepper flakes. Season with salt and pepper to taste. Mix until everything is well combined.
Take each shell and fill it with the ricotta mixture, about 2 tablespoons per shell. Place the stuffed shells upright in a 9x13 inch baking dish.
Pour marinara sauce evenly over the stuffed shells, ensuring each shell is well-coated.
Sprinkle the remaining mozzarella cheese over the top of the sauce-covered shells.
Cover the dish with aluminum foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 10-15 minutes until the cheese is bubbly and golden.
Remove from the oven and let the dish cool for a few minutes. Garnish with fresh basil leaves before serving.
Notes
Feel free to adjust the amount of red pepper flakes based on your spice preference.