Preheat a frying pan over medium heat. Add the avocado oil and heat until shimmering. Add the tomatillos, onion, garlic, and jalapeño and cook, stirring occasionally, until the vegetables are lightly charred. Add the water and cook, using a wooden spoon to lift any brown bits off the bottom of the pan, until the liquid has reduced by ¼ in volume and the tomatillos are fork-tender, around 3 minutes.
Add everything to a blender along with the cilantro, lime juice, oregano, salt, and avocado and pulse until as smooth or chunky as you prefer. Taste the salsa for seasoning and adjust with salt and lime juice as desired. Transfer the salsa to a bowl, cover, and refrigerate until ready to serve. The salsa will last up to 3 days in the fridge.
In a bowl, combine the steak, orange juice, lime juice, ¼ cup chopped cilantro, paprika, salt, onion powder, black pepper, smoked paprika, ground cumin, and oregano. Toss everything to coat, cover, and refrigerate 1 to 6 hours.
When ready to cook, preheat your grill to 500F (475F if using a grill grate) or a heavy-bottomed skillet or griddle over medium-high heat. If using a grill, add the avocado oil to the steak and toss to coat. If using a skillet or griddle, add the avocado oil to the pan and heat until shimmering. Transfer the steaks and green onions onto the grill or skillet/griddle and cook, undisturbed, until grill marks form or deeply seared, around 4 minutes for the steak and 2 minutes for the onion. Flip and cook the other side until grill marks form or deeply seared and the thickest part of the steak registers 125F for a medium-rare center, around 4 more minutes for the steak and 1 minute for the onion. Transfer the steak and green onions to a cutting board and let them rest at least 6 minutes before slicing the steak into small cubes, leaving the onions whole.
While the steaks rest, warm the tortillas on the grill or skillet/griddle for 10-15 seconds per side. Alternatively, place a heat-safe wire rack over a gas stovetop and warm the tortillas directly over the open flame, 10-15 seconds per side.
In a small bowl, combine the remaining ¼ cup chopped cilantro and diced white onion and toss to incorporate.
To assemble the tacos, spread a layer of diced steak onto each tortilla, top with some of the avocado salsa, and garnish with the fresh cilantro and onion mixture. Serve with the charred green onions, extra avocado salsa on the side, and lime wedges for squeezing.