Prep the oven or skillet: Preheat the oven to 400°F (205°C) and line a sheet pan with parchment.
If pan-searing, heat a large skillet over medium heat with 1 tablespoon olive oil.
Mix the base: In a large bowl, add ground chicken, Parmesan, breadcrumbs, egg, garlic, parsley, Italian seasoning, onion powder, salt, pepper, and milk. Stir gently with a fork until just combined. Do not overmix to keep the meatballs tender.
Form meatballs: Lightly oil your hands. Scoop about 2 tablespoons of mixture and roll into balls, about 1 1/2 inches wide.
Place on the prepared sheet pan or a plate if searing.
Bake method: Brush the tops with a little olive oil. Bake 14–18 minutes, until the centers reach 165°F (74°C). For extra color, broil 1–2 minutes at the end.
Pan-sear method: Add meatballs to the hot skillet without crowding.
Sear 2–3 minutes per side until golden, then reduce heat, cover, and cook 5–7 more minutes, turning occasionally, until they reach 165°F (74°C).
Optional garlic-butter finish: Melt 1 tablespoon butter in the skillet. Add a pinch of red pepper flakes and a little minced garlic, swirl for 30 seconds, then toss meatballs to coat. Finish with lemon zest and extra Parmesan.
Serve: Garnish with parsley and more Parmesan.
Enjoy with pasta and marinara, over creamy polenta, tucked into toasted rolls, or alongside a simple salad.