Shrimp Tacos with Pineapple

Name: Shrimp Tacos with Pineapple
Ingredients: 1/2 small red onion, thinly sliced; 2 tablespoons fresh lime juice; Pinch of sugar; Kosher salt; 1/4 medium pineapple, peeled, cored, cut lengthwise into spears, then crosswise 1/2 thick (about 2 cups); 2 tablespoons extra-virgin olive oil, divided; 1 1/4 pounds shrimp, peeled, deveined; 1 tablespoon Sriracha; Freshly ground black pepper; 8 corn tortillas, warmed; 1 avocado, sliced; 1 jalapeño, very thinly sliced, seeds removed if desired; 1/2 cup cilantro leaves with tender stems; Lime wedges (for serving)