Slice onion very thin, on a mandoline if you have one. Place in a bowl, season with salt and pepper and pour vinegar over top. Stir to combine and set aside.
Toss the cabbage with mayonnaise to taste. Season with salt and pepper, cover and refrigerate until ready to serve. Just before serving, add 1 of the vinegar that the onions are marinating in.
In 2 small bowls, stir together about 1/2 cup of mayonnaise with 1 tablespoon of HURRICANE SRIRACHA SAUCE and ½ cup of mayonnaise with 1 tablespoon CHIPOTLE LIME SAUCE.
Set the oven to broil. Slice the buns in half, and spread each cut side lightly with butter. Place under the broiler, cut side up, until lightly browned 2-3 minutes.
Cut the fish into 6 pieces each, about the size of the slider buns. Trim the thin parts of the fish if necessary, so pieces are uniform in thickness. Place on a parchment paper lined sheet pan and brush each piece of salmon with the HURRICANE SRIRACHA SAUCE and each piece of halibut with the CHIPOTLE LIME SAUCE. Season with salt and pepper. Broil until cooked through, watching closely so they don’t burn on top, 8-10 minutes, depending on thickness.
Set the bottom halves of the buns on a serving platter. Slather 6 with the HURRICANE SRIRACHA mayonnaise, and 6 with the CHIPOTLE LIME mayonnaise. Top with spinach or lettuce or shredded cabbage, fish, pickled onions and feta cheese. Serve immediately.