Preheat the oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Prepare the tzatziki by whisking 1 cup Greek yogurt, grated cucumber, lemon juice, and fresh dill in a small bowl. Season with a pinch of salt and refrigerate.
In a large mixing bowl, combine ground turkey, 1/2 cup Greek yogurt, egg, panko, feta, red onion, garlic, parsley, oregano, salt, and pepper.
Gently mix the ingredients by hand until just combined; do not overwork the meat to maintain a tender texture.
Scoop and roll the mixture into 1.5-inch balls, yielding approximately 16 to 20 meatballs.
Arrange meatballs on the prepared baking sheet, ensuring they do not touch.
Bake for 18 to 20 minutes, or until the internal temperature reaches 165°F (74°C).
Remove from oven and let rest for 5 minutes before serving with the chilled tzatziki sauce.