Rinse well and drain the kidney beans and cannellini beans.
Chop your green beans into bite-sized pieces if desired.
Place the kidney beans, cannellini beans, and thawed green beans in a large bowl.
Add the sliced onion to a small bowl of cold water for about five minutes then drain the water. This step helps to tame down the onions a bit.
Add the onions and your chopped parsley to the large bowl with the beans.
In a separate bowl, whisk together the vinegar, olive oil, sea salt, pepper, and thyme to create a dressing.
Pour this dressing over the beans, onion, and parsley.
Stir to combine.
Cover then transfer your bean salad to the fridge and let the beans marinate in the dressing for about 30 minutes.
Give the salad a good stir just before serving.
Enjoy!