Place a rack in the oven 6 to 8 inches away from the heater element. Preheat broiler to high.
Combine chili powder, cumin, ¾ teaspoon kosher salt and ½ teaspoon black pepper in a small bowl. Pat fish dry and coat with spice mixture. Arrange fish filets on a foil-lined baking sheet and spread each filet with 1 tablespoon of Challenge Spreadable Butter.
Broil for 5-6 minutes, or until the fish is just cooked through and crispy on the edges. Spread each filet with remaining 1 tablespoon butter, then cut in half and place on a warmed corn tortilla. Top with shredded cabbage, cilantro and a dollop of sour cream. Squeeze with fresh lime juice and serve.