Drain beans into a colander and rinse until no foaming remains. Let drain well. Mix dressing ingredients, then put the beans into a ziptop bag, shake. Let marinate in dressing one hour or longer. Halve grape tomatoes. Dice onions and chop cilantro. Combine beans with dressing, tomatoes, green onions and cilantro. Stir gently until combined. Season with salt and pepper. Serve immediately.