In a large skillet, add the pork butt, salt, black pepper, lemon pepper, oregano and garlic and cook for 10 minutes.
Add the Salsa Verde, cilantro, cumin, green chiles and onions and cook for another 5 minutes.
Transfer to a slow cooker, cover and cook on high for 30 minutes, and then turn down to low and cook for 3 hours to 3 hours 30 minutes.
In a saucepan, boil the tomatillos, garlic, jalapenos, serrano pepper and half of the onions in 2 cups of water until the mixture floats to the top of the saucepan, about 30 minutes. Strain out the pulp and reserve the liquid. In a food processor, blend the pulp with the remaining onions, the cilantro, salt and 3/4 cup of the reserved liquid.