In a large dish, layer the onion, cucumber, serrano pepper, cilantro, and tomato.

Drizzle everything with lemon pepper, lime juice, Maggi seasoning, and Worcestershire sauce.

Let it sit while you finely shred the smoked tuna.

Add the tuna to the dish and mix all the ingredients well.

Serve cold on tostadas with chipotle mayo and top with diced avocado.