Preheat oven to 450° F. Line a baking sheet with parchment paper or foil. Spray it with cooking oil.
In a large bowl whisk together the panko, parsley, grated onion, garlic, lemon zest and juice, egg, spices, salt and pepper, and feta.
Add the ground beef to the mixture and combine with your hands being careful not to over-work the meat mixture. Form approximately tablespoon sized meatballs.
Place the meatballs on the prepared baking sheet and spray or brush the tops with olive oil. Place the baking sheet on the center rack of the oven and bake for approximately 10-12 minutes or until golden brown.
Make the tzatziki sauce while the meatballs are baking by combining all of the ingredient in a medium sized bowl and stirring together until combined.
Remove the meatballs from the oven and serve with the tzatziki sauce.
