Place the fish in a resealable bag or container. Combine the beer, chili powder, brown sugar, salt, cumin, garlic and lime zest and juice in a large bowl. Give it a good stir and pour it over the fish. Marinate the fish for 30 minutes in the refrigerator.
Preheat a grill or grill pan over medium-high heat.
Take the fish out of the marinade and pat dry completely. Brush the fish with the oil and grill until browned, 3 to 4 minutes per side. Transfer to a plate, cover with foil and let rest for 5 minute. Slice each fillet into slices.
Heat the tortillas on the grill for about a minute, or wrap them in a damp towel and microwave until warm, soft and pliable, about 1 minute.
Spread some of the Carlsbad Cream onto the warmed tortillas. Place a few slices of fish on top of each and then top with some cabbage and Pickled Red Onions. Serve with lime wedges on the side.
Combine the sour cream, mayonnaise, hot sauce, salt and lime zest in a medium bowl and stir. Cover and refrigerate until ready to use.
Pickled Red Onions:
Whisk the vinegar, sugar and salt together in a mixing bowl until the sugar and salt have dissolved. Add the oregano and onions, cover and allow to rest for 2 hours. Store in a jar or resealable glass container in the refrigerator for up to a month.