Preheat the oven to 400°F.

Line a large baking sheet with parchment paper. Set aside.

Season the steaks liberally on both sides with the salt, black pepper, and garlic powder. Allow them to rest at room temperature while preparing the pepper and onions.

Slice the bell peppers and onion into 1/4-inch strips and transfer to the prepared baking sheet.

Drizzle the bell pepper and onion slices with olive oil and season with the salt and black pepper. Toss to coat, and arrange in an even layer.

Roast the peppers and onions on middle rack of oven for 25 minutes. At the 20 minute mark, begin searing the steaks.

Set a large skillet over high heat and add the oil and butter. Once oil is very hot and shimmering, add the steaks. Sear steaks for 1 minute without moving, then flip and sear other side for 45 seconds longer.

Open the oven and clear a space in the middle of the baking sheet with tongs or a rubber spatula. Transfer the seared steaks from the skillet to the cleared space. Arrange some of the peppers and onions over the steaks. Close oven and continue roasting steaks, peppers, and onions until vegetables are browned, and steaks reach an internal temperature of at least 130°F for medium doneness, 9-12 minutes.

Check to see that dish is done. Remove from oven or add time as needed.

Allow the steaks and vegetables to rest for 5 minutes before serving.