Tangy shrimp tostadas

Ingredients

• 455 grams cooked peeled shrimp, diced
• 1 avocado, diced
• 1/2 English cucumber, diced
• 1/4 red onion, finely diced
• 1/2 jalapeño pepper, minced
• 1/4 cup chopped fresh cilantro
• 1 navel orange, zest and juice
• 1 lime, juice
• 8 tostadas shells
• Salt and freshly ground black pepper