Make the pickled onions. In a large jar add onions, water, apple cider vinegar, and 1 teaspoon salt. Shake well and set aside.
Make the mahi mahi burgers. Roughly cut mahi mahi and add half to a food processor. Pulse 3-4 times until broken down, but still a little chucky and some texture remains. I did this in two batches to make sure it didn't get too mushy.
Add mahi mahi to a bowl with the almond flour, egg, taco seasoning, and salt and pepper. Mix to combine and form into 4 equal sized patties. The mixture will be fairly wet. Coat each patty with a little more almond flour on each side.
Heat up a large sauté pan over medium-low heat. Add oil and let it get hot. Add burgers, spreading them out evenly, and cook for 3-4 mintues per side until golden brown and cooked through.
While the burgers cook, make the cabbage slaw by mixing together the cabbage, cilantro lime juice, and salt and pepper. Prep the rest of your toppings if needed.
Divide cabbage slaw, avoacdo, and pickled onions among the burgers and top with chipotle mayo. Enjoy!
To save some time, you can make the pickled onions on advance. They will be more pickled that way too!