Cook the pasta shells in a large pot of salted boiling water per the package instructions, slightly undercooking. Drain well, then spread in a single layer on a piece of parchment paper. (The shells can stick together as they cool.)
Preheat the oven to 350°F. Spray a 13x9-inch baking dish or pan with nonstick cooking spray.
Drizzle a large skillet with olive oil. Cook the ground beef and onion over medium-high heat until no pink remains in the beef. Drain excess grease from the pan.
To the ground beef, add the salsa, taco seasoning, chili powder, seasoned salt, garlic powder and lemon pepper. Stir to combine, then add the cream cheese.
Simmer on low stirring just until the cream cheese has completely melted. Remove from the heat, add 1 1/2 cups shredded cheese. Stir until evenly distributed.
Use a tablespoon to divide the ground beef mixture between the shells, around 1 1/2-2 Tbsp each. Arrange side by side seam side up in the prepared dish.
Drizzle the taco sauce over the shells, then sprinkle the top with the remaining 1 1/2 cups shredded cheese.
Baked uncovered for 35-45 minutes until bubbly and the cheese is lightly golden brown.
Let stand for 5 minutes, then serve topped with sour cream and salsa garnished with green onions, olives and diced tomatoes.
Cook's Note: Servings may vary depending on how many shells are used. Some shells will break while boiling. You may end up with 30-36 stuffed shells.