Open the cans of black beans, kidney beans, and chickpeas. Pour them into a colander and rinse under cold water. Let them drain well.

Chop the cherry tomatoes in half, finely chop the red onion, and chop the bell pepper into bite-sized pieces. Chop the fresh parsley.

In a small bowl, combine olive oil, red wine vinegar, lemon juice, minced garlic, and Dijon mustard. Whisk until well blended. Add salt, pepper, and cumin to taste.

In a large mixing bowl, add the drained beans, chopped cherry tomatoes, red onion, bell pepper, and parsley. Pour the dressing over the top and gently toss to combine.

If using avocado, fold it in carefully to avoid mashing. Cover and chill in the refrigerator for about an hour for best flavor.

Serve the salad as a main dish or side, garnished with additional herbs or cheese if desired.