In a medium mixing bowl, combine the avocado oil, orange zest, juice from the 3 oranges, minced fresh garlic, onion powder, garlic powder, smoked paprika, cumin, 1 Tbsp of salt, and 1 tsp of black pepper. Mix and add the steak to marinate for 30 minutes to 12 hours.
15 minutes before cooking, preheat the grill to medium high. In a small bowl, combine the sliced serrano chilis with 2 tsp lime juice and 1 pinch salt. Mix and set aside.
Make the guacamole by peeling the avocado, discarding the skin and pit, and mashing it. Add 1-2 Tbsp lime juice, 1 tsp garlic powder, a pinch of salt and a few grinds of black pepper. Stir to combine, cover and refrigerate.
Make the slaw by combining the sliced cabbage, bell pepper, green onion, and chopped cilantro. Toss together with 2 Tbsp lime juice, 2 Tbsp extra virgin olive oil, 2 pinches of salt and a few grinds of black pepper.
Grill the steaks for 6 minutes. 4 minutes on the first side, rotating 90 degrees 2 minutes into the cook, another 2 minutes, flip, then another 2 minutes. Test the temperature and it should be around 130-140. Remove and allow to cool.
If using corn tortillas, warm them in a pan first. If using lettuce, wash the leaves and pat dry.
Assemble the tacos by first adding a layer of guacamole (onto the lettuce or tortilla), then steak, slaw, crema, Serrano chilis (if desired - they're spicy), salsa (if desired), and crumbled cotija cheese.