In a bowl, combine thin strips of beef with cumin, chili powder, minced garlic, and a splash of olive oil. Let the beef marinate for at least 30 minutes.

While the beef marinates, slice the bell peppers and onions into thin strips. Set them aside.

Heat a skillet over medium-high heat. Add the marinated beef strips and sear for about 3-4 minutes until browned.

Remove beef from skillet and let it rest. In the same skillet, sauté the bell peppers and onions for about 5 minutes until tender.

Warm tortillas briefly, then assemble by placing beef and vegetables onto tortillas. Top with guacamole, sour cream, or cilantro.