Bring a large pot of water to boil. Add 1 tsp. salt, then green beans, and simmer until crisp-tender, 3 to 4 minutes. Immediately transfer to a bowl of ice water to cool, about 5 minutes. Drain and pat dry.  Meanwhile, heat oil in a medium skillet on medium. Add garlic and cook, stirring, until just beginning to brown, about 1 minute. Stir in tomatoes and cook, tossing occasionally, until just beginning to split, 3 to 4 minutes. Remove skillet from heat and toss with orange juice, vinegar, and sesame oil, then sesame seeds and orange zest.   In a large bowl, toss green beens with chickpeas, cannellini beans, and scallions. Just before serving, toss beans with tomato mixture and 1/2 tsp. each salt and pepper.