Preheat the oven to 425 degrees F and coat a lidded baking sheet with nonstick cooking spray.
Combine chopped onion, garlic, parsley and breadcrumbs in a food processor and mix 30 seconds.
Break the egg into a 3-quart bowl and mix well using a wire whisk. Add water, olive oil, salt, pepper, and nutmeg to the egg and whisk until blended.
Add the bread crumb mixture, combining with a spatula.
Add the ground meat and mix thoroughly until ingredients are well distributed and the mixture is binding together.
Using a medium sized ice cream scoop, scoop out a portion onto a lightly oiled cookie sheet. Form each meatball by rolling in the palm of your hand until they feel tight and solid. (The finished meatballs should be about the size of a golf ball.)
Pour 1/4 cup water into the pan and place in the oven. Bake 15 minutes. Remove from the oven and loosen with a spatula. Return to the oven an additional 10 minutes, or until cooked through. Drain.