Shrimp Ceviche Cocktail

chopped red onion

small limes, squeezed

olive oil

large cooked shrimp, peeled and deveined*

medium hass avocado, diced into chunks

medium tomato, diced

diced English cucumber, not peeled

serrano pepper, seeds removed and minced

chopped cilantro, plus more for garnish

salt and fresh black pepper

lime cut into wedges for serving

shredded iceberg lettuce