Mushroom “Carnitas” Tacos

Name: Mushroom “Carnitas” Tacos
Ingredients: 1 small red onion; 1/2 cup seasoned rice vinegar; 1/3 cup water; 1/3 cup regular or vegan mayonnaise; 1 to 4 tablespoons canned chipotle peppers in adobo sauce, such as La Morena or La Costena; 12 (about 5-inch) corn tortillas; 2 medium avocados; 1 1/4 pounds enoki mushrooms; 1 teaspoon ground cumin; 1 teaspoon garlic powder; 1 teaspoon smoked paprika; 3/4 teaspoon kosher salt; 1/4 teaspoon freshly ground black pepper; 4 tablespoons olive oil, divided