In a large dish, combine the olive oil, juice from one lime, taco seasoning, and salt. Transfer the flank steak to the marinade and toss to coat both sides. Cover and marinate in refrigerator for at least an hour.
In the meantime, slice the onion and bell peppers, and jalapeno. Prep the tortillas and the toppings.
In a large skillet, over medium heat, add about a tablespoon of olive oil into the skillet and sear the steak 2-3 minutes each side until desired doneness. Transfer to cutting board to rest. Toss the veggies into the same skillet adding a bit more oil if the skillet is dry. Saute until cooked, yet still slightly firm.
Slice steak just before serving. Serve with the tortillas and toppings.