Preheat oven to 350°F (175°C).

Heat olive oil in a large skillet over medium-high heat. Add sliced onions and bell peppers to shimmering oil. Cook them until they're soft and lightly caramelized.

Add the sliced steak to the skillet, seasoning it with garlic powder, salt, and pepper. Cook until the sirloin is browned and cooked through (5–7 minutes).

Dump the mixture into a greased baking dish. Incorporate cheese and proceed to bake for a duration of 10 to 15 minutes, or until the mixture becomes bubbly and attains a golden hue.

Let rest briefly before serving (implied in the article’s closing notes about avoiding a runny texture).