Place the Marinated Beef ingredients in a ziplock bag, massage to coat then refrigerate for 2 hour to overnight.
Remove beef from marinade 30 minutes prior to cooking (to bring to room temperature) and pat dry with paper towels. Discard marinade.
Drizzle ½ tbsp of oil on each side of the beef (1 tbsp in total).
Heat the BBQ or a skillet on high heat. Cook beef to your liking.
Remove beef onto a plate and cover loosely with foil.
Return skillet to stove, still on high heat, and heat ½ tbsp oil. Add onions, sprinkle with salt and pepper, and cook until soft and charred. Remove onto serving plate.
Heat remaining ½ tbsp oil in the skillet. Add bell pepper/capsicum, sprinkle with salt and pepper, and cook until charred. Remove onto plate.
Slice beef thinly against the grain.
Serve with warmed tortillas and fixings of choice.
