Mediterranean Tuna Salad with a Zesty Dijon Mustard Vinaigrette

good quality Dijon mustard

Zest of 1 lime

limes, juice of

Early Harvest extra virgin olive oil

sumac

salt and pepper

crushed red pepper flakes, optional

Genova tuna in olive oil

celery stalks, chopped

English cucumber, chopped

whole small radishes, stems removed, chopped

green onions, both white and green parts, chopped

medium-sized red onion, finely chopped

cup pitted Kalamata olives, halved

bunch of parsley, stems removed, chopped (about 1 cup chopped fresh parsley)

fresh mint leaves, stems removed, finely chopped (about 1/2 cup chopped fresh mint)

slices heirloom tomatoes for serving

Pita chips or pita pockets for serving