Heat a large skillet (preferably a cast iron skillet) over medium-high heat.
Drizzle beef strips with half the marinade and then sear in skillet for 2-3 minutes on each side until slightly browned/blackened. When done, remove from pan and set aside in a bowl.
In the same skillet over medium-high heat, sear the veggies drizzled with the remaining marinade. Toss occasionally and cook until tender but slightly firm and slightly browned (about 5 minutes).
Throw meat back in the pan, toss to combine, and serve.
Assemble fajitas by placing meat & veggies on a warm tortilla and top with fresh lime juice, avocado slices, salsa, cheese, and cilantro.