Prepare pickled onions and crema at least 1 hour in advance
Preheat oven to 100°C (212°F) to keep cooked tacos warm
To make crema: In a bowl, whisk vegan sour cream with lime juice, smoked paprika, 1/2 tsp salt, and 1/2 Tbsp of preserved lemon zest. Mix well and refrigerate
To make pickled onions: In a saucepan, combine 125ml white grape juice + 50ml balsamic vinegar. Add red onions, 1/2 cup preserved lemon zest, and crushed red pepper. Simmer for 5 minutes, cool, then refrigerate 30 minutes
Dry salmon skin thoroughly with paper towels. In a bowl, mix chickpea flour with 1 tbsp salt and black pepper
Heat 1 Tbsp avocado oil in ovenproof skillet over medium-high heat. Pat salmon dry and dredge in chickpea flour mixture, shaking off excess
Sear salmon skin-side down for 5 minutes. Flip and cook for 1-2 minutes until cooked through, moving to oven mid-cook if browning too fast
Warm tortillas in oven: Place on baking sheet, drizzle with 2 Tbsp oil in a V shape around edges, and warm for 2-3 minutes until pliable
Assemble tacos with salmon, pickled onions, crema, and optional shredded cabbage
Serve immediately with lime wedges