Preheat oven to 450F.
Prepare flank steak by seasoning with 2 tablespoons of the fajitas seasoning mix.
Drizzle 1 tablespoon olive oil over steak and turn to coat.
Cut a large piece of aluminum foil; set steak in the center of the foil and fold up the sides so it holds in the juices.
Place the prepared steak on a sheet pan and set aside.
Drizzle prepared vegetables with remaining 1/2 tablespoon olive oil and toss with remaining fajitas seasoning mix.
Add peppers and onions to sheet pan.
Cook for 13 to 15 minutes, or until steak's internal temperature is 140F.
Set under the broiler for 2 to 3 minutes, or until steak's internal temperature is at least 145F.
Remove from oven and let steak rest for about 5 to 8 minutes before slicing.
Sprinkle with parsley or cilantro and a squeeze of fresh lime juice.
Serve with warm flour tortillas.
Optional: add sour cream, shredded cheese and avocado.