Preheat the oven to 425 degrees F (218 degrees C). Line a baking sheet with parchment paper or foil (grease if using foil).
In a large bowl, stir together the grated Parmesan cheese, sunflower seed meal, Italian seasoning, sea salt, and black pepper.
Whisk in the milk, grated onion, egg, garlic, and fresh parsley. Let the mixture sit for a couple of minutes.
Mix in the ground beef using your hands, until just incorporated. (Don’t over-mix to avoid tough meatballs.)
Form the mixture into 1 in (2.5 cm) balls and place on the lined baking sheet. (A small cookie scoop works well for this. If using your hands, use a gentle touch and don’t pack the meatballs too tightly.)
Bake for 10-12 minutes, until the meatballs are barely done. (If you want them more golden, you can place them under the broiler for a couple of minutes.)
Top each meatball with marinara sauce. Return to the oven and bake for 3-5 minutes, until the sauce is hot and meatballs are cooked through. Garnish with additional fresh parsley.