Make the salsa verde. Add the tomatillos, jalapeños, and garlic to a large baking sheet. Roast directly under the broiler for 10 minutes, flipping halfway through, until the tomatillos and peppers are charred. Add the roasted vegetables along with onion, cilantro, lime juice, and salt to a large blender and blend until smooth. Set aside.
Make the guacamole. Cut the avocados in half and remove the pit with a sharp knife. Scoop out the fruit using a spoon and transfer it into a medium mixing bowl. Mash the avocados until it reaches your desired consistency. Stir in the chopped cilantro, tomato, onion, lime juice, jalapeño, and salt. Taste and adjust the seasoning as needed, then set aside.
Make the carne asada. In a medium bowl, combine chopped sirloin steak with olive oil, soy sauce, and seasonings until well coated.
Sauté steak in a large skillet over medium-high heat until all the juices have evaporated and the steak begins to caramelize, about 8-0 minutes. Transfer to a separate bowl and set aside.
Assemble and serve the vampiro tacos. In the same skillet used for the carne asada, heat 2-3 corn tortillas at a time over medium heat, flipping every 1-2 minutes for 10 minutes until the tortillas are crispy and browned, almost like a tostada. Sprinkle ¼ cup of shredded cheese on each tortilla and allow it to melt for about a minute.
Add carne asada, salsa verde, guacamole, cilantro, and onion on top of the crispy cheese tortilla and serve immediately.
Notes
Crisping the tortillas. Toasting the tortillas in the same skillet as the carne asada adds extra flavor, but you can also use a separate skillet, a comal, an open flame on a gas stove, or a grill. The trick is to slowly crisp the tortilla until it's extra crunchy.
Other filling ideas. Tacos vampiros usually feature a hearty topping like carne asada, but you can use whatever you prefer or have on hand, like chicken, chorizo, beans, or nopales.