Adjust an oven rack to the middle position and heat the oven to 200°. Pour the oil into a large, deep, heavy-bottomed pan until oil measures 3 inches deep. Heat the oil over medium-high heat until it reaches 375°. While the oil heats, whisk the flour, salt, cumin, black pepper, and cayenne together in a large bowl. When the oil is almost ready, whisk the beer into the flour mixture until completely smooth. Wrap a stack of corn or flour tortillas in foil and warm on a baking sheet in the 200° oven while frying the fish. Pat the fish dry with paper towels, Add half the fish to the batter and coat. Use tongs to transfer the fish from the batter, one at a time, to the hot oil. Fry, stirring the fish gently to prevent the pieces from sticking together, until golden brown (about 5 minutes). Remove the fried fish from the oil and let drain briefly on paper towels. Transfer the drained fish to the oven to keep warm. Batter and fry the remaining fish. Smear each of the warm tortillas with 1 tablespoon of Spicy Mayonnaise; add shredded cabbage, tomatoes, and avocado. Add 1-2 pieces of the fried fish to each tortilla and garnish with lime wedges and cilantro.