Preheat the broiler to 500 degree F. In a small bowl, whisk the oil, fajita seasoning, and garlic.
On a rimmed baking sheet, toss the steak, bell pepper and onion with the spiced oil until well-mixed.
Broil, turning once, until the vegetables are browned in spots and the meat is charred and cooked to desired doneness, 8 to 10 minutes. Give care not to burn the fajitas - broiler temperatures can vary greatly.
Serve the steak and vegetables in tortillas.
Notes
Recipe adapted from Rachel Ray (link no longer available)