Preheat your oven to 375°F (190°C).

Arrange the halved bell peppers in a baking dish, cut side up, and drizzle with olive oil. Roast for 10 minutes to soften.

While the peppers are roasting, heat a skillet over medium-high heat and add olive oil.

Add the sliced onion and mushrooms to the skillet, and sauté until the onions become translucent and the mushrooms are tender, which should take about 5 minutes.

Incorporate the thinly sliced beef into the skillet, seasoning with garlic powder, salt, and pepper. Cook until the beef is browned and fully cooked, approximately 5-7 minutes.

Remove the peppers from the oven and fill each half with the beef mixture.

Place a slice of provolone cheese on top of each stuffed pepper.

Return the peppers to the oven and bake for an additional 10 minutes, or until the cheese has melted and is bubbly.

Serve hot and enjoy!