Dice red bell pepper, English cucumber, and red onion; halve cherry tomatoes; chop fresh parsley.
Rinse and drain chickpeas, cannellini beans, and kidney beans in a colander under cold water.
In a small bowl, whisk together extra virgin olive oil, red wine vinegar, Dijon mustard, minced garlic, salt, and black pepper until emulsified.
In a large mixing bowl, combine drained chickpeas, cannellini beans, kidney beans, diced vegetables, halved cherry tomatoes, and chopped parsley.
Pour dressing over the bean and vegetable mixture and gently toss until evenly coated.
Cover the bowl and refrigerate for at least 30 minutes before serving.