Preheat the oven to 350°F. Spray a 9 x 13 inch glass baking dish with cooking spray.
Cook the shells per the instructions on the box in salted water until al dente, then drain and cool slightly.
In a stove top pan, saute the chopped onion in a couple of tablespoons of olive oil, until translucent. Add the ground beef to the pan and cook until no pink remains. Season with salt and pepper to taste.
Drain excess fat from the pan. Add the sun dried tomatoes, pesto, Worcestershire sauce, minced garlic, Italian seasoning, and red pepper flakes to the ground beef. Stir until combined.
Add the whipped cream cheese, ricotta cheese spinach Simmer on low heat for 2 minute or just until melted. Taste and adjust salt and black pepper to your taste. Remove from the heat.
Add egg, 1 cup of Italian cheese blend and 1/3 cup of grated Parmesan cheese. Stir thoroughly.
Fill shells using a tablespoon then place side by side, seam side up in the dish. Drizzle the tops with the marinara sauce.
Bake for 35-40 minutes or until heated through and bubbly. Place the remaining shredded cheese on top five minutes before the end of baking.