Drain and rinse your canned beans thoroughly under cold water until the water runs clear. This removes excess sodium and that slightly metallic taste. If using dried beans you've cooked yourself, let them cool completely before proceeding. Pat the beans dry with paper towels to prevent a watery salad.

Dice the bell peppers into uniform ½-inch pieces for consistent texture and visual appeal. The key here is keeping everything roughly the same size as your beans. Finely chop the red onion – you want flavor without overwhelming crunch. Remove the cucumber seeds before dicing to prevent excess moisture from making your salad soggy.

Whisk together olive oil, red wine vinegar, Dijon mustard, minced garlic, and oregano in a small bowl. The mustard acts as an emulsifier, helping create a creamy, cohesive dressing that clings beautifully to the beans. Season generously with salt and pepper – beans need more seasoning than you might think.

Add the prepared beans and chopped vegetables to a large mixing bowl. Pour the dressing over everything and toss gently but thoroughly. Fold in the fresh parsley last to maintain its vibrant color and prevent bruising.

Allow the salad to sit for at least 30 minutes at room temperature, or refrigerate for 2 hours. This resting period lets the beans absorb the tangy dressing while the flavors marry beautifully. Taste and adjust seasoning before serving – you might need an extra pinch of salt or splash of vinegar.