Rinse the Kalamata and green olives under cool water in a colander, then pat them dry with a clean kitchen towel to remove excess moisture.

Using the flat side of a knife, gently crack each Kalamata olive, remove the pits, halve the olives, and transfer them to a large mixing bowl.

Chop the green olives into roughly quarter-inch pieces and add them to the mixing bowl with the Kalamata olives.

Slice the celery stalks lengthwise, dice into small even pieces, and add to the olive mixture.

Dice the red bell pepper into pieces similar in size to the celery and add to the bowl.

Chop the roasted red peppers into similar-sized pieces, drain if packed in oil, then add to the bowl.

Smash and mince the garlic cloves finely, then add them to the bowl.

Chop the fresh parsley, then add parsley, capers, dried oregano, and red pepper flakes to the mixture.

In a small bowl, whisk together extra virgin olive oil, red wine vinegar, and Dijon mustard until the dressing is emulsified.

Pour the dressing over the olive and vegetable mixture and stir with a wooden spoon until everything is well coated.

Season with salt and black pepper to taste, cover the bowl, and let the salad rest at room temperature for at least 30 minutes to allow flavors to meld.