Prep your setup: Line a sheet pan with parchment for easy cleanup.
Lightly oil it if baking. If pan-searing, set a large nonstick or stainless skillet on the stove.
Combine the wet mix-ins: In a large bowl, whisk the egg, yogurt, grated onion (and its juices), garlic, salt, pepper, oregano, and red pepper flakes. Stir in the parsley and parmesan.
Add chicken and breadcrumbs: Add the ground chicken and breadcrumbs to the bowl.
Mix gently with a fork or your hands until just combined. Do not overmix—that’s how you keep the texture tender.
Shape the meatballs: Lightly oil your hands. Scoop about 1 1/2 tablespoons per meatball and roll into smooth balls. You should get around 20–24 small meatballs.
Choose your cooking method: To bake: Heat oven to 425°F (220°C).
Arrange meatballs on the sheet pan and brush or mist lightly with olive oil. Bake 12–15 minutes, until just cooked through (165°F/74°C inside). Broil 1–2 minutes for extra browning if you like.
To pan-sear: Heat 2 tablespoons olive oil over medium heat.
Add meatballs in a single layer, not crowding the pan. Cook 7–9 minutes total, turning to brown all sides, until center reaches 165°F (74°C).
To simmer in sauce: Lightly brown the meatballs in a skillet for 3–4 minutes, then nestle them into warm marinara. Cover and simmer on low 8–10 minutes, until cooked through.
Rest briefly: Let meatballs sit 3 minutes before serving.
This helps the juices settle.
Serve: Spoon over sauce, pair with buttered noodles, tuck into a sub, or pile onto fluffy rice with a squeeze of lemon.