To make the marinade: Place all the ingredients in a blender and blend until smooth. Place the steak and marinade in a plastic bag. Seal the bag and refrigerate for at least 3 hours, up to overnight.

Heat a large skillet on medium-high heat and warm 1 tablespoon of the olive oil. Add the bell peppers, onion, salt and pepper, and cook until tender, about 8 to 10 minutes. Transfer to a plate.

Using a damp paper towel, wipe out the skillet. Keeping the heat on medium-high, warm 1 Tablespoon olive oil.

Remove the steak from the marinade and cut into ½-inch-thick slices.

Place the steak in the skillet. Cook, turning once, 3 to 4 minutes per side for medium-rare, or until done to your liking.

eturn the peppers and onion to the skillet and stir together to warm through.

To assemble the fajitas, place a warmed tortilla on a plate. Add a few slices of steak, some peppers, onion and sour cream, if using, and sprinkle with cilantro. Serve with rice, beans, guacamole and salsa on the side

Repeat to assemble the remaining fajitas.