Marinate chopped napa or savoy cabbage in white balsamic vinegar, fennel seed, 1/2 teaspoon oregano, and salt at least 2 hours or in the fridge overnight.
Make some pickled green tomato slices using your favorite pickling recipe that’s slightly sweet (this can be done 1 day ahead of time).
Heat the skillet over high heat until it’s very hot and add grapeseed oil (or olive oil or butter). Season each side of the fish with a mix of 1/2 teaspoon oregano, paprika, cayenne, salt and pepper.
Sear the fish on each side to get a crust, about 2-3 minutes per side. Butter a brioche bun on each side and toast it in the same skillet to get the edges crispy.
Make chile aioli by mixing mayonnaise, chile oil, garlic, and lemon juice. Adjust the ratio of ingredients to your taste. Store the excess in the fridge for later!
Smear on both sides of the bun, add the cabbage, the fish and the pickled green tomatoes and serve with crispy potatoes or salad.