Nopales and Shrimp Tacos

Name: Nopales and Shrimp Tacos
Ingredients: ½ cup avocado , chopped; ½ cup fresh chopped cilantro; ¼ cup sour cream; ¼ cup water; ½ serrano chile , seeded and minced; 1 teaspoon lime juice; ¼ teaspoon table salt; 1 pound nopales (4 to 5 paddles); ¼ teaspoon plus ⅛ teaspoon table salt , divided, plus salt for salting vegetables; 6 ounces grape tomatoes , quartered; ⅓ cup finely chopped white onion; ¼ cup fresh chopped cilantro; 4 teaspoons extra-virgin olive oil , divided; 1 teaspoon grated lime zest plus 2 teaspoons juice, plus lime wedges for serving; 1 pound extra-large shrimp (21 to 25 per pound), peeled, deveined, and tails removed, halved lengthwise; 1 garlic clove , minced; 12 (6-inch) corn tortillas , warmed