Shrimp Tostada with Avocado Salsa - Rick Bayless

Ingredients

• 12 ounces medium cooked shrimp, peeled and deveined
• 1 medium white onion, cut into 1/4-inch pieces, rinsed under cold running water and drained
• 1 medium-large round or 2 to 3 plums (about 8 oz) ripe tomatoes, cut into ¼ inch pieces
• 1/4 to 1/3 cup fresh lime juice
• Fresh hot green chile to taste (usually 3 serranos or 1 to 2 jalapeňos), stemmed and roughly chopped
• 1 medium avocado, pitted, flesh scooped from the skin
• 1/3 cup (loosely packed) roughly chopped cilantro (thick bottom stems cut off), plus extra for garnish
• Salt
• 12 store-bought tostadas