Preheat oven to 350°. Clean mushrooms and remove stems. With a spoon, gently scrape out the gills (the dark brown striated flesh on the underside of the mushroom). Place in a 9 x 13 baking dish. Set aside.
Combine beef, chopped mushroom stems and Onion Onion™ Seasoning in a large skillet over medium-high heat. Cook and crumble until beef is no longer pink. Drain. Remove from heat and stir in rice and ½ cup cheese. Fill mushroom caps. Sprinkle with remaining cheese and bake 25 minutes.
Always check the labels of ingredients in recipes to confirm they are gluten-free, and ensure your space is free from other possible sources of gluten. Since ingredient formulas can change and vary among other brands, Tastefully Simple cannot ensure that prepared recipes will be gluten-free.