Cook the orzo in boiling salted water for 5-7 minutes and drain.
In a large bowl combine the onion, garlic, tuna, feta cheese, black olives, cannellini beans, tomatoes, green pepper and black pepper and toss well to combine.
Fold in the cooked orzo.
Whisk together the vinaigrette dressing, oregano and red pepper flakes and add to the salad ingredients, mixing gently to combine.
To serve sprinkle with chopped mint and garnish with slices of cucumber and grape tomatoes.
Serves 4-6