In a resealable plastic bag, combine the pineapple juice, 1 tbsp (15 mL) lime zest, 1/4 cup (60 mL) lime juice, canola oil, Worcestershire sauce, brown sugar, cloves garlic, and 1 tsp (5 mL) each salt and pepper. Seal the bag, then massage the bag so the marinade coats everything evenly. Add the 1/2 lb flank steak, press out excess air, seal again, and turn to coat. Refrigerate for at least 4 hours or up to overnight, turning occasionally so the steak marinates evenly.

Preheat grill to medium-high; grease the grate well so the steak and pineapple don’t stick. Grill the flank steak for 4 to 5 minutes per side for medium-rare or to desired doneness, watching for good grill marks and a nicely browned exterior. Transfer the steak to a cutting board, tent loosely with foil if desired, and let stand for 10 minutes so the juices redistribute; then slice thinly across the grain. Meanwhile, grill the pineapple for 5 to 8 minutes or until grill-marked and lightly caramelized. Let the pineapple cool slightly, then dice into small pieces for the tacos.

In a small bowl, stir together the sour cream, remaining lime zest, remaining lime juice, and remaining 1/4 tsp each salt and pepper until smooth and well blended to make a lime sour cream. Fill taco shells with a layer of thinly sliced flank steak, 1/4 cups thinly sliced red cabbage, diced grilled pineapple, and slices or chunks of ripe large avocado. Drizzle each taco with the lime sour cream, then sprinkle with finely chopped fresh cilantro and thinly sliced red chili pepper just before serving.