Using your hands, tear 2 pounds oyster mushrooms into strips and place into a large bowl.
Combine 1/2 cup cornstarch, 1 teaspoon onion powder, 1 teaspoon garlic powder, 1 teaspoon ancho chili powder, 1 teaspoon ground cumin, 1 teaspoon kosher salt, and 1/2 teaspoon ground cinnamon in a separate medium bowl. Whisk until well combined.
Toss the mushrooms with the cornstarch mixture until well coated.
Mix together the 1/4 cup orange juice, 1 tablespoon lime juice, 1 clove minced garlic, 1/2 teaspoon dried oregano, and 1/4 teaspoon ground black pepper in a separate medium bowl.
Warm the tortillas, mince the onions and the cilantro, and prep any other garnishes. Keep the tortillas warm in a tortilla warmer or wrapped in a clean kitchen towel.
Fry the mushrooms in batches, heat 1/4 cup of avocado oil in a large frying pan over medium-high heat. Once the oil is hot add just enough mushrooms to cover the bottom of the pan, but not crowd. Cook, letting them brown nicely on the bottom before turning. Continue cooking until they are browned and crispy on all sides, about 5-6 minutes.
Transfer to a large bowl and repeat with another batch of mushrooms. I used a 14-inch frying pan and cooked the mushrooms in three batches.
Once all the mushrooms are fried, return all of them to the frying pan and place of medium-high heat. Add the orange juice mixture and toss to coat.
Tuck into warm corn tortillas and top with minced onion and cilantro. Serve immediately so they don't lose thier crispiness.