Thaw fish overnight in the refrigerator if frozen.
Mix the fish rub, ground cumin, and chile powder in a small dish.
When you’re ready to cook, pat fish dry with paper towels, then rub both sides with 2 tsp. of the olive oil followed by the fish rub mixture.
Let the fish come to room temperature while you prep the other ingredients.
Cut away the core of the cabbage and discard, then use a knife or a Mandoline Slicer (affiliate link) to cut the cabbage into thin slices; we used the 3 cm blade for the mandoline. (You can also use pre-sliced coleslaw mix if you don’t want to bother cutting the cabbage.)
Thinly slice the green onion.
Whisk together the mayo, lime juice, Green Tabasco Sauce, and Vege-Sal (or salt) to make the dressing (affiliate links).
Brush a stove-top grill pan or heavy frying pan with the other 2 tsp. olive oil and heat the pan about a minute at medium-high heat. Then add the fish and cook about 4 minutes on the first side.
Turn gently and cook about 4 minutes more on the other side. (Actual cooking time will depend on how thick your pieces of fish are. Fish should feel barely firm to the touch when it’s done.)
While the fish cooks, mix about half the green onions into the cabbage mixture and stir in enough dressing to barely moisten the cabbage.
When the fish is done, let it cool slightly on a cutting board, then use two forks to shred the fish apart.
Fill bowl with 1/4 of the cabbage mixture and top with desired amount of fish. Drizzle a little more dressing over the top.
Serve right away, with green onions for garnish and guacamole if desired.