For the Chicken Parm Meatballs:

1. Preheat the oven to 350°F.
2. In a large bowl, combine 1 tbsp olive oil, panko, parmesan, egg, grated onion, garlic, parsley, Italian seasoning, red pepper flakes, black pepper, and salt. Mix until combined. Add the ground chicken and mix until incorporated. 
3. Using a 2” cookie scoop or spoon, form the mixture into golf ball-sized meatballs. Stuff each with a mini mozzarella ball, sealing the chicken mixture completely around the cheese so it doesn’t leak while cooking. 
4. Heat an oven proof skillet over medium heat and drizzle in 2 tbsps olive oil. Once hot, add half the meatballs in a single layer and cook for 3-4 minutes, turning to brown on all sides. Transfer to a plate and repeat with the remaining meatballs (they won’t be fully cooked at this stage, as they will finish cooking in the oven).
5. Reduce the heat to low. Return all meatballs to the skillet and pour in the marinara sauce, gently turning to coat. Shut off the heat.
6. Top with sliced mozzarella and parmesan cheese. Transfer to the oven and bake for 15-20 minutes, until the meatballs are cooked through. Broil on high for the last 2 minutes, until the cheese is melted and bubbly.
7. To make the optional breadcrumb topping (best for serving with pasta), heat butter in a small skillet over medium heat. Once melted and starting to bubble, add in the grated garlic and stir until softened. Add the panko breadcrumbs and toss to coat in the garlic butter. Cook for 2-3 minutes, stirring often, until golden brown. Remove from heat and stir in fresh parsley. 
8. To serve, spoon the meatballs over pasta and top with the garlic butter breadcrumbs just before serving for extra crunch — or enjoy straight from the skillet with crusty bread and skip the breadcrumbs altogether.