Mix seasonings together and apply liberally to both sides of the steak. Alowl to sit and come to room temperature to avoid the meat shrinking and becoming tough on grill. I usually eyeball my seasonings, but I am estimating the amount I use in the measurements above.
Cut and seed green bell pepper, rub with oil and season with salt and pepper. Cut ends off of onion and peel skin, coat with oil salt and pepper and wrap completely with aluminum foil.
As soon as fire dies down on charcoal grill place your onion on the coals. This will need the most time to cook so as soon as I can I place it in the heat.
Once coals are ready place flank steaks on grill. This meat is lean so there are not normally many flare ups from the fire. Allow meat to cook approx 10 minutes on each side, flipping only once. You want the meat to have a medium center so that it will retain moisture and juiciness. Once you have flipped the meat add your peppers to the grill and char each side. Remove meat from grill and let rest for about 10-15 minutes tented with foil so that juices can recirculate.
Cut steaks in thin strips with a SHARP knife on the bias Cut peppers and onions into strips.
Serve on tortillas and top with cheese, lettuce, sour cream, diced tomatoes, and salsa.