In a large salad bowl, combine: sliced cucumber, sliced avocado, thinly sliced red onion, drained tuna, and ¼ cup cilantro
Drizzle salad ingredients with 2 Tbsp lemon juice, 2 Tbsp olive oil, 1 tsp salt and ⅛ tsp black pepper (or season to taste). Toss to combine and serve.
