Scyros (Pita Sandwich)
1 bunch fresh spinach, cleaned and stemmed 1 large red onion, thinly sliced 1 pinch dried oregano, or to taste 1 pound ground beef 2 stalks celery, chopped 2 tablespoons olive oil 2 tomatoes, cut into wedges 3 large cloves garlic, minced 5 pita breads, warmed ½ cucumber - peeled, seeded and finely choppe… ½ cup banana pepper rings ½ cup plain yogurt ½ cup sliced fresh mushrooms ½ teaspoon chopped fresh dill, or to taste