Set up a vegetable steamer. When the water is boiling, add the green beans and cook until just slightly tender and still crisp. Immerse the beans in an ice bath to stop the cooking and drain.
If desired (to minimize the raw onion taste), put the finely chopped red onion in a bowl covered with the vinegar and place in the refrigerator for 20 minutes to soak. Drain and rinse.
Mix together 2 Tb of the lemon juice, garlic, salt, and pepper. Slowly stream the olive oil into the mixture and whisk to emulsify. Add most of the dill and stir well to combine.
In a large bowl, combine the onion, green beans, kidney and garbanzo beans. Add half of the dressing and stir to combine; continue to add more dressing to your liking. Taste for lemon flavor and add remaining lemon if desired, as well as salt and pepper. Sprinkle remaining dill on top to garnish and serve either chilled or at room temperature.
This salad keeps well refrigerated for a few days, may need "freshening up" with more lemon juice.