Pour oil into a 5- to 6-quart pan over medium-high heat. When hot, add pork and stir often until browned on all sides, about 12 minutes. Transfer pork to a plate.
Add onion, mushrooms, and garlic to pan. Stir often until onion is limp, about 5 minutes. Add enchilada sauce, salsa, and pork to pan and bring to a simmer. Lower heat and cook, stirring occasionally, until pork is no longer pink in the center (cut to test), about 15 minutes. Spoon into bowls.