Slice flank steak thinly against the grain (tip: this is easier to do if the steak is still slightly frozen in the middle). Add steak to a large container or ziploc bag and set aside.
Prep the marinade. Add the avocado oil, garlic, and spices to a small bowl. Zest the orange & limes into the bowl, then squeeze the juice from the fruit into the bowl. Chop half of the cilantro (save the other half for toppings) and add to the marinade. Whisk to combine, then pour over the steak, stirring to evenly coat. Seal the steak and place in the fridge for at least 2 hours, if not overnight.
Prep the fajita veggies by thinly slicing the bell peppers & white onion. Slice the jalapenos into rings. Refrigerate veggies in a large Tupperware container until ready to cook.
Preheat your Blackstone to high. Add 1-2 tbsp avocado oil to the griddle and spread the oil out into a thin layer, then toss your veggies onto the flat top. Cook, tossing frequently, until soft and lightly charred. Scoop up the veggies onto a platter to remove from the heat. Set aside.
Pour your marinated steak onto the flat top and cook until no longer red in the middle and you reach your desired level of doneness, about 5-7 minutes.
Remove meat from the flat top and place on the platter with the vegetables. Serve with tortillas and your favorite toppings, like avocado, cilantro, cheese, and sour cream.
Video
Notes
Store leftovers in an airtight container in the fridge. Eat within 3-4 days.