Preheat oven to 400 F and coat 9-by-13-inch baking dish with olive oil.
In skillet, brown ground turkey with minced garlic, onion, garlic powder and cumin until meat is cooked, 4-5 minutes.
With small knife, cut eyes, nose and mouth into flattest side of each pepper to resemble jack-o’-lantern. Cut around seed pods and remove pepper tops, trimming and discarding any seeds from under stems then setting tops aside. Trim white membranes from inside each pepper and shake out seeds. Place peppers in prepared baking dish.
In bowl, combine turkey mixture with cooked rice, cheddar cheese, salt, black pepper and cayenne pepper, to taste.
Divide and stuff mixture into peppers; cover with reserved pepper tops.
Wrap baking dish loosely with aluminum foil and bake until peppers are tender, about 45 minutes.
Spoon about 3 tablespoons warm tomato sauce onto each plate; place stuffed peppers on top. Serve remaining sauce on side.