In a medium bowl, whisk together mayonnaise or plain yogurt, taco seasoning, and fresh lime juice until thoroughly combined. Add shredded cabbage, red cabbage, grated carrots, sliced green onions, and chopped cilantro to the mixture. Toss until the veggies are evenly coated. Set aside some dressing for later and let the slaw marinate for about 10 minutes.

Pat the cod fillets dry with paper towels and season generously with salt and pepper. In a large skillet, heat a tablespoon of oil over medium-high heat until shimmering. Carefully place the fillets into the skillet and cook for about 4 minutes on each side, or until the fish flakes easily and turns golden brown. Remove from skillet and let rest.

In the same skillet, add more oil if needed and heat over medium-high heat. Sauté chopped red onion, diced red bell pepper, and minced jalapeño for about 1 minute. Stir in thawed corn, drained black beans, and a sprinkle of taco seasoning, cooking for an additional 2-3 minutes. Finish with a splash of fresh lime juice and sliced green onions.

To assemble the bowls, start with a layer of slaw in each bowl, followed by warm salsa. Place cooked cod fillets on top, then add sliced avocado. Garnish with lime wedges and more cilantro.