Preheat your oven to 350°F. Cook your jumbo shells in salted water until al dente. Drain them and set them aside to cool slightly. Cook your bacon until crispy, then crumble it into small pieces. Shred your cooked chicken.
Combine the shredded chicken, softened cream cheese, sour cream, ranch seasoning, and crumbled bacon in a large mixing bowl. Mix until everything is evenly incorporated.
Using a spoon or piping bag, fill each shell generously with the chicken mixture. Place the stuffed shells in a greased 9×13-inch baking dish.
Sprinkle a mix of shredded mozzarella and cheddar cheese over the shells. The cheese will melt into a golden, bubbly topping.
Cover the dish with aluminum foil and bake for 20 minutes. Remove the foil during the last 5 minutes for a perfectly browned top.
Once baked, garnish your shells with diced green onions, a drizzle of ranch dressing, and diced tomatoes if desired. Serve warm.