Preheat an indoor or outdoor grill to medium-high. Brush the steak with 1 Tbsp. of the oil; season with salt and pepper. Cook the steak to the desired doneness. Allow 2 to 3 minutes per side for rare, 3 to 4 minutes for medium-rare, and 4 to 5 minutes for medium. While the steak grills, place the remaining oil in a large, non-stick skillet and set over medium-high heat. Add the onion and bell peppers and cook 2 minutes. Mix in the chili powder, cumin, cayenne, salt and pepper and cook 1 to 2 minutes more, then reserve on low heat.
When cooked, remove the steak from the grill and set on a cutting board. Cool a few minutes and then thinly slice and arrange on a small platter. Spoon the onion/bell pepper mixture into a serving bowl and place it, the sliced steak, and the remaining ingredients, each in separate serving dishes, on the table and allow diners to create their own fajitas