Grilled Shrimp Tacos with Pickled Onions

Name: Grilled Shrimp Tacos with Pickled Onions
Ingredients: 1/2 cup white wine vinegar; 2 tsp. sugar; Kosher salt and freshly ground black pepper; 1 serrano chile, seeded, finely chopped; 1/3 cup sour cream; 1 tsp. finely grated lime zest; 2 Tbsp. fresh lime juice; ¼ head green cabbage, thinly sliced (about 3 cups); 1 1/2 lb. medium shrimp, peeled, deveined, halved lengthwise; 1 Tbsp. olive oil; ¾ tsp. chipotle chile powder; 3/4 tsp. ground cumin; 8 corn tortillas; 1/2 medium red onion, thinly sliced; Cilantro sprigs, sliced avocado, lime wedges, and hot sauce (for serving)