Preheat the oven to 375°F (190°C). Line a large rimmed baking sheet with parchment paper.
In a large bowl, whisk together the whole-wheat flour, baking powder, and salt.
Add the Greek yogurt and tablespoon of olive oil. Stir until a dough forms, then knead gently for 1–2 minutes. Add a teaspoon of water if it is dry or a little flour if it is excessively sticky.
In a separate bowl, combine the turkey ham, mozzarella, bell pepper, green onions, Dijon mustard, garlic powder, and black pepper.
Divide the dough into 16 equal portions. Flatten each portion into a small disc about 2½–3 inches wide.
Place a small spoonful of filling in the center of each disc. Bring the edges together and pinch firmly to seal, then roll gently into a ball.
Arrange the dough balls seam-side down in a ring on the prepared baking sheet, leaving a little space between the pieces.
Brush lightly with olive oil or beaten egg if desired.
Bake for 25–30 minutes, checking at 22 minutes, until the dough is golden and cooked through. If the top browns too quickly, cover it loosely with foil and continue baking.
Rest for 5 minutes before serving. Garnish with chopped parsley or green onions if desired.