To make the frying flour combine the flour, chile powder, oregano, salt and cumin in a large bowl, and mix very well. The flour keeps in an airtight container stored in a dry, dark place for a few weeks.
To make the tacos put the fish in a large bowl, add 1 tablespoon of the lime juice and the salt, and toss well. Put the frying flour in another large bowl, add the fish, and toss very well to evenly coat the fish.
Pour 3 inches of canola oil into a Dutch oven or medium pot and heat the oil over medium-high heat until it reaches 375F on a deep-fry thermometer. Working in batches to avoid crowding the oil, shake off a little flour from the fish, then add the fish to the oil and fry until the pieces are lightly golden brown and crispy, about 2 minutes per batch. Transfer the fried fish to a paper towel to drain.
When the fish is just cool enough to handle, put it in a large bowl and add the onions, cilantro, chiles, Worcestershire sauce, olive oil, and the remaining 2 tablespoons of lime juice. Toss and mix well with your hands or a spoon, breaking up the strips into small pieces as you do. Season to taste with more lime juice, chiles, and salt.
Serve with warm tortillas with lime wedges, avocado, crema and green salsa on the side.