Wash all fresh vegetables under cold running water. Dice the Roma tomatoes, cucumber, and bell pepper into bite-sized pieces. Finely slice the red onion and set aside in a large mixing bowl.

Add the Kalamata olives and chopped fresh parsley to the bowl with the diced vegetables. Toss gently with a wooden spoon.

In a small bowl, combine olive oil, red wine vinegar, Dijon mustard, and minced garlic. Whisk together for about 30 seconds until emulsified.

Adjust salt and pepper to taste. Pour the dressing over the salad and mix to coat evenly.

Drizzle the dressing over the salad mixture and toss gently. Serve fresh as an appetizer or side dish.