Bring a large pot of salted water to a boil. Add the 12 large pasta shells and cook according to package instructions until just al dente, usually around 8-10 minutes. Drain and rinse under cold water to stop the cooking process. Set aside on a clean kitchen towel to dry.
In a large mixing bowl, combine the shredded chicken, cooked turkey bacon, ranch dressing, softened cream cheese, 1 1/2 cups shredded cheddar cheese, garlic powder, onion powder, salt, and pepper. Stir until all ingredients are well incorporated and creamy.
Carefully fill each cooked pasta shell with a generous spoonful of the chicken and bacon mixture. Arrange the stuffed shells in a greased baking dish, placing them snugly side by side to prevent tipping.
Sprinkle the remaining 1/2 cup shredded cheddar cheese evenly over the top of the shells. Cover the baking dish with foil and bake in a preheated oven at 350°F (175°C) for 20 minutes. Remove the foil and bake uncovered for another 5-10 minutes until the cheese is bubbly and golden.
Remove the shells from the oven and let them cool slightly. Sprinkle sliced green onions on top for a fresh, colorful garnish. Serve warm and enjoy!