1/3 cup extra-virgin olive oil
3 cloves garlic, minced
1 teaspoon dried mint (optional)
1 teaspoon dried oregano
1/2 teaspoon paprika
Kosher salt and freshly ground pepper
1/2 cup 2% plain Greek yogurt
1 green bell pepper, seeded and sliced into 1/2-inch-thick rings
1 onion, sliced into 1/2-inch-thick rounds
1 pound skirt steak
4 pocketless pitas
1 tomato, chopped
1 bunch watercress, roughly chopped
Preheat a grill to medium high.
Make the marinade: Whisk the olive oil, garlic, mint (if using), oregano, paprika, 1 teaspoon salt, and pepper to taste in a large bowl.
Transfer 1 tablespoon of the marinade to a small bowl; mix in the yogurt and 2 tablespoons water. Add the bell pepper and onion to the bowl with the remaining marinade and toss; remove to a plate with a slotted spoon. Add the steak to the bowl and toss.
Grill the bell pepper, onion and steak, turning once, until lightly charred, about 4 minutes per side for the vegetables and 4 to 8 minutes per side for the steak (depending on the thickness). Set aside to rest, about 5 minutes.
Meanwhile, grill the pitas until marked, about 1 minute per side.
Slice the steak against the grain. Fill the pitas with the steak, grilled vegetables and tomato.