Prepare the slaw by mixing the shredded cabbage, shredded carrots, chopped cilantro, vegan mayonnaise, lime juice, salt, and pepper in a bowl. Toss everything together until the slaw is well coated. Set it aside in the refrigerator to chill while you prepare the "fish."
In a shallow bowl, whisk together the flour, garlic powder, paprika, salt, and black pepper. In another bowl, pour the plant-based milk.
Heat a generous amount of vegetable oil in a skillet or frying pan over medium-high heat. You'll want enough oil to submerge the "fish" fillets.
Dip each vegan fish fillet into the plant-based milk, allowing any excess to drip off, and then coat it in the flour mixture, pressing lightly to adhere to the batter. Carefully place the battered fillets into the hot oil and fry until they are golden brown and crispy, about 3-4 minutes per side. Transfer the cooked fillets to a paper towel-lined plate to remove excess oil.
Warm the tortillas in a dry skillet or microwave them according to the package instructions.
To assemble the tacos, place a spoonful of the slaw on each tortilla, followed by a vegan "fish" fillet. Add avocado slices if desired, and squeeze fresh lime juice over the top. Drizzle with hot sauce if you like it spicy.
Serve the vegan fish tacos immediately, with extra lime wedges and hot sauce on the side for those who want an extra kick.