Easy Shrimp Ceviche

Name: Easy Shrimp Ceviche
Ingredients: 1 pound peeled and deveined raw medium shrimp, thawed if frozen; 1/4 cup freshly squeezed lemon juice (from 2 lemons); 1/4 cup freshly squeezed lime juice (from 2 to 3 limes); 2 medium tomatoes, seeded and chopped; 1/2 small red onion, finely chopped; 1 medium jalapeño, seeded and finely chopped (about 3 tablespoons); 1/2 cup chopped fresh cilantro leaves and tender stems; 1/2 teaspoon kosher salt; 1 medium avocado; Tostadas or tortilla chips, for serving (optional)