Fill a large bowl with ice and cold water and set aside. Slice a thin piece from the bottom of each pepper to stop peppers from rolling onto their sides when baking.
Bring a large pot of water to a boil over medium-high heat. Drop each pepper carefully into the water and boil 2 minutes. Remove peppers from water and place in the bowl of ice water.
Cook turkey sausage in a skillet over medium heat until browned, about 3 minutes. Drain excess fat. Stir in Cheddar cheese, cream cheese, Parmesan cheese, ranch-flavored seasoning, and garlic.
Remove peppers from water and drain. Fill each pepper with sausage mixture, forming a mound. Place filled peppers on a baking sheet; place in the freezer until just frozen, about 20 minutes.
Preheat the oven to 350 degrees F (175 degrees C).
Mix bread crumbs with butter. Press into the top of the sausage filling.
Bake in the preheated oven until bread crumbs are golden brown and cheese starts to bubble, 25 to 30 minutes.