In a small bowl, whisk together mayonnaise (or yogurt), taco seasoning, and fresh lime juice until smooth.

In a medium bowl, combine shredded cabbage, shredded carrots, sliced green onions, and chopped cilantro. Drizzle in about ¼ cup of the dressing, gently tossing to coat all ingredients evenly. Set aside.

Pat the cod fillets dry and brush with olive oil. Season generously with taco seasoning and cook in a skillet over medium-high heat for about 4 minutes. Flip and cook for another 3-4 minutes.

In the same skillet, add olive oil and sauté diced red onion, chopped red bell pepper, and minced jalapeño for 1 minute. Add corn and black beans, cooking for 2 more minutes and adding lime juice and green onions.

To assemble, divide the prepared slaw among bowls, spoon on the salsa, top with cooked cod and sliced avocado. Serve immediately.