Toss tomatoes, cucumber and 1/2 tsp salt together in colander and let drain for 20 minutes.

Whisk oil, vinegar and garlic in large bowl. Measure 2 Tbsp vinaigrette into another bowl and toss with tuna and 1 Tbsp. parsley.

Add drained tomatoes and cucumber. Add chickpeas, olives and onion and let sit for 5 mins. Add lettuce, feta and remaining parsley and toss to combine. Top with tuna and serve.