Peel the husks from the tomatillos (1), rinse off the sticky coating (2), then quarter, core and chop (3). In a food processor, pulse all the green salsa ingredients to finely chop; season with salt.
In a small bowl, mix all the sriracha crema ingredients.
For the tacos, in a large skillet, heat the oil, two turns of the pan, over medium-high. Cook the pork, stirring occasionally and breaking up with a spoon, until browned, about 8 minutes. Add the onion, garlic and oregano; season with salt and pepper. Cook, stirring often, until the onion softens, 2 to 3 minutes. Add the stock; reduce the heat to medium-low. Cook until thickened, 7 to 8 minutes.
In a large, dry skillet over high heat or directly over the open flame on a gas stovetop, cook the tortillas, turning occasionally, until charred in spots, about 2 minutes.
Slather the sriracha crema on the tortillas and top with the pork mixture, cheese, lettuce, green salsa and pickled jalapeño slices.