Whipped this up for a recent event and they were hands down the best appetizer at the party

Preheat the oven to 400 F.
Place a large skillet over a medium-high heat. Add the olive oil and heat until shimmering.
Add the mushroom stems, onion, pepper, garlic and spices. Sauté until the vegetables begin to soften.
Add the ground beef and smash down as you continue to sauté.
Once no more pink is visible, remove the skillet from the heat and fill each mushroom cup up to the top with the beef mixture.
Sprinkle each with shredded cheese and place on a foil-lined baking sheet.
Bake 15 minutes, or until the cheese has melted.
Allow to cool 5 minutes before serving.