Mix the fish sauce ingredients in a bowl, cover and refrigerate till needed. Cut up the tomato(s) and set aside on a small plate. (I don’t bother with peeling and seeding the tomatoes).
In a bowl, mix together the 1½ Tbs lime juice, 2 Tbs olive oil and 2 tsp of minced jalapeno pepper. Rinse the fish under cold water, pat dry, place in the bowl and toss to coat, cover with plastic wrap and refrigerate till the grill is hot.
Heat a gas grill or a charcoal grill to medium-high heat.
Scrape off any jalapeno particles from the fish and lightly sprinkle chili powder on both sides of the fish, if you wish. Oil the grill grate and grill the fish over medium-high heat till the fish flakes easily, turning after 4 minutes, about 10 minutes total cooking time. Cut the fish into 8 equal portions, wrap in foil and keep warm in a preheated oven set to 170°F.
Warm each flour tortilla on the grill till soft, wrap in foil and keep warm in the oven. Make a fluid assembly line of the ingredients: taco shells, fish, sauce, coleslaw, tomatoes, tortillas and refried beans. Ready a large platter and a roll of aluminum foil, place a portion of fish into a crispy taco shell, top with some sauce, coleslaw mix, tomatoes and optional cucumber slivers. Place on the platter. Repeat with the remaining crispy taco shells. Now smear some warm black refried beans onto a flour tortilla and wrap it around one of the tacos. Wrap each double-decker taco in foil so to keep warm. Repeat with the remaining tortillas and tacos.
Serve with lime wedges, corn on the cob and a cold fruit salad on the side. Serve beer and/or fruit daiquiris as beverages.
* TIP: Place the interior side of the cut jalapeno peppers facing down on the cutting board when mincing them so to prevent squirts of jalapeno juice striking you in the face. NEVER touch your face while dealing with jalapenos. Wash your hands thoroughly after handling jalapenos. It’s no fun getting jalapeno juice in your eyes.