Mix together the fajita seasoning, olive oil, and lime juice. Put the steak in a gallon-sized ziptop bag. Add the marinade. Seal and place in the fridge to marinate for 6 hours or overnight.
Slice the bell peppers and onions into wedges. Place in a gallon-sized ziptop bag. Add the zesty Italian salad dressing. Seal and place in the fridge to marinate for 6 hours or overnight.
Remove the steaks and veggies from the plastic baggies and place on the grill over medium heat. Throw away the marinade. Grill for 12-17 minutes or until the steak reaches an internal temperature of 160˚F.
Cut the steak into slices. Serve with flour tortillas, grilled veggies, and other toppings.