Pre-heat the oven to 400 °F, and lightly grease a baking dish.
In a bowl, add the ground chicken, onion, garlic, breadcrumbs, egg, Dijon mustard, lemon zest & juice, rosemary, Parmesan, salt and pepper.
Blend with a fork or your hands until the mixture is well blended, and sticks together. If it's too wet, you can add a little more of the breadcrumbs, bit by bit, until you achieve the desired texture.
Use a spoon to create meatball rounds. As they are formed, placed them in the greased baking dish.
Drizzle with olive oil, and bake for about 10 to 12 minutes as you make the sauce.