Step 1: Pat the fish fillets very dry with paper towels. In a small bowl, combine the chili powder, cumin, paprika, garlic powder, onion powder, salt, and black pepper. Rub this spice mixture generously over both sides of the fish fillets.
Step 2: Heat a large non-stick skillet or cast-iron pan over medium-high heat. Add the olive oil. Once the oil is shimmering, carefully place the seasoned fish fillets in the pan. Cook for 3-4 minutes per side, or until the fish is opaque, cooked through, and flakes easily with a fork. Remove from the pan and flake into bite-sized pieces.
Step 3: Prepare the lime crema. In a small bowl, whisk together the Mexican crema (or sour cream), fresh lime juice, chopped cilantro, and a pinch of salt. Taste and adjust seasoning as needed.
Step 4: Prepare your remaining bowl components. Wash and thoroughly dry the romaine lettuce, then chop it. Dice the red onion, tomatoes, and avocado. Shred the cabbage thinly. Drain and rinse the black beans and corn. Set all these vibrant ingredients aside.
Step 5: To assemble the bowls, start with a base of chopped romaine lettuce in each bowl. Arrange the flaked fish over the lettuce. Artfully add spoonfuls of black beans, corn, diced tomatoes, diced avocado, and shredded cabbage around the fish.
Step 6: Drizzle a generous amount of the prepared lime crema over all the ingredients. Garnish with extra fresh cilantro, a wedge of lime, and a sprinkle of cotija cheese, if desired. Serve immediately.