How to Make It
In a food processor, process the chopped cucumber until minced. Transfer to a kitchen towel. Squeeze out as much liquid as possible and transfer the cucumber to a bowl.
In the food processor, combine the yogurt, roasted peppers, garlic, dill and 2 tablespoons of the vinegar and process until smooth. Add the yogurt mixture to the drained cucumber and stir well. Season the tzatziki with salt and pepper.
In a large bowl, combine the remaining 1 tablespoon of vinegar with the olive oil and oregano. Add the Kirby cucumber, olives, peperoncini, radishes, tomatoes, mustard greens, onion and feta and toss well. Season with salt and pepper.
Spread about 2 tablespoons of tzatziki onto each bread and top with the salad. Serve right away.