Bonappetit greek salad

3 tbsp extra-virgin olive oil
3 tbsp red wine vinegar
2 tsp dijon mustard
2 tsp dried oregano
kosher salt and freshly ground pepper
1 large cucumber
1 med green pepper
1 small red onion
variety of tomatoes
kalamata olives, pitted
1 tbsp capers, drained
feta cheese in brine, cut into thin slabs
extra sprinkle of oregano