Prepare the cabbage slaw by tossing the shredded green cabbage, red cabbage, and carrots in a large mixing bowl.
In a small bowl, whisk together the mayonnaise, sour cream, and lime juice. Pour the dressing over the cabbage mixture, toss until evenly coated, and refrigerate.
Pat the fish fillet strips completely dry with a paper towel.
Set up a three-bowl breading station: combine the flour and taco seasoning in the first bowl, place the beaten eggs in the second, and pour the panko breadcrumbs into the third.
Dredge each piece of fish in the seasoned flour, dip it into the beaten eggs, and finally press it firmly into the panko breadcrumbs to coat completely.
Heat the vegetable oil in a large, heavy-bottomed skillet over medium-high heat until it reaches 350°F (175°C).
Fry the breaded fish strips in batches for 3 to 4 minutes per side, until golden brown and cooked through. Transfer to a paper towel-lined plate to drain excess oil.
Warm the tortillas in a dry skillet over medium heat for 30 seconds per side.
Assemble the tacos by placing 1 to 2 pieces of fried fish in the center of each tortilla. Top generously with the creamy cabbage slaw, garnish with fresh avocado slices, and serve immediately with lime wedges.