In a large bowl, whisk together mayonnaise (or yogurt), taco seasoning, and fresh lime juice until smooth. Add the shredded cabbage, red cabbage, shredded carrots, sliced green onions, and chopped cilantro to the mix. Toss everything together until the veggies are well-coated in the dressing.

Pat the cod fillets dry with paper towels. Brush both sides with olive oil and season with taco seasoning. Heat a skillet over medium heat, add olive oil, and cook the fillets for about 4 minutes until browned, then flip and cook for another 3-4 minutes until flaky.

In the same skillet, sauté diced red onion, red bell pepper, and jalapeño over medium heat for 1 minute. Add frozen corn and black beans, cooking for another 1-2 minutes. Squeeze fresh lime juice and sprinkle with chopped green onions.

To assemble, divide the slaw among serving bowls, top with salsa, place cod fillets, and finish with avocado slices and lime wedges.