Avocado Tuna Salad

15 oz (o 3 maliit na lata) na tuna sa mantika, pinatuyo at tinupi
1 English cucumber
1 maliit/med na pulang sibuyas, hiniwa
2 avocado, diced
2 Tbsp extra virgin olive oil o sunflower oil
Juice ng 1 medium lemon (mga 2 Tbsp)
¼ cup (1/2 bungkos) cilantro, tinadtad
1 tsp sea salt o ¾ tsp table salt
⅛ tsp black pepper