Bring medium pot filled with water to boil over medium-high heat. Add green beans; cook until beans are heated through, turn bright green and are crisp-tender, about 5 minutes. Add onions to colander. Strain green beans in colander with onions; rinse under cold water until cool; drain well.
In large bowl, whisk together olive oil, vinegar, mustard and Adobo until well combined. Gently stir in cannellini beans, chickpeas, red kidney beans and green bean-onion mixture. Gently toss to combine; cover and refrigerate until beans are chilled and seasoned through, about 2 hours. Serve chilled or room temperature