Make the vinaigrette first. Whisk together the olive oil, lemon juice, red wine vinegar, Dijon, minced garlic, salt, and pepper.
Rinse and drain the cannellini beans. Thinly slice the red onion and roughly chop the parsley.
Place the beans, onions, and parsley in a bowl, then pour the vinaigrette over top. Stir to combine. Taste and adjust the salt or pepper to your liking.