Aside from making carnitas, this is the other thing we do with pork butt. When I grabbed a can of green enchilada sauce, I made the mistake (?) of reading the ingredients:
Water, Green Chiles, Green Tomatoes, Vinegar, Modified Food Starch, Salt, Soybean Oil, Garlic, Sugar, Spices, Dry Onion, Monosodium Glutamate, Onion Powder, Hydrolyzed Soy Protein, Corn Starch, Textured Soya Protein (Soy Flour, Hydrogenated Vegetable Oil, Salt, Nat & Art. Flavors), Natural & Artificial Flavors, Colors (Annatto, Fd&C Yellow #5 and 6), Yeast Extract, Calcium Silicate (Anticaking Agent), Garlic Powder, Disodium Inosinate and Guanylate), Citric Acid. Contains:Soy.
So, we made our own. It was just a hodge podge of peppers we bought at the market. We roasted everything on the barbecue (for the sauce), peeled, then pureed.
I eat mine in a bowl with a teaspoon of sour cream, grated cheese, chopped onion and cilantro on top.