Preheat & Prep. To start, preheat oven to 375 degrees F. Set out an 8x8 or 9x9 baking pan. (I like a ceramic pan or glass pan for this.)
Combine. In a large bowl, combine ground chicken breast, breadcrumbs, parmesan cheese, basil, garlic, salt, pepper, and Italian seasoning. Use a fork or clean hands to gently mix until just combined.
Divide & Roll. Divide the mixture into 16 meatballs. (I use a medium cookie scoop for this!) If desired, tuck a mozzarella pearl or cube into the center of each meatball, then roll smooth in between your hands.
Brown Meatballs. Heat olive oil in a large skillet. Working in batches (I cook 1/2 the meatballs at a time!), brown meatballs 2-3 minutes per side, just till golden brown. The meatballs will NOT be fully cooked through at this point.
Bake. Pour 1 1/3 cup of marinara into the baking pan. Tuck the browned meatballs into the marinara, then top with remaining 2/3 cup marinara sauce. Sprinkle with grated mozzarella cheese. Bake in preheated oven 20-25 minutes, or until the interior of the meatballs reaches 165 degrees F. Garnish with more basil, parmesan, or black pepper, if desired.
Serve & Store. Enjoy warm with pasta, buns, or garlic bread and a side salad or veggies. Store leftover meatballs covered or in an airtight container in the fridge 3-4 days.