Step 1: Preheat the Oven and Mix the Meatballs - Preheat your oven to 400°F. In a large mixing bowl, add the ground chicken, breadcrumbs, shredded mozzarella, 1/4 cup pesto, black pepper, garlic powder, salt, and egg. Use clean hands to gently mix everything together until the ingredients are evenly distributed. Try not to squeeze or knead the mixture more than necessary. Ground chicken is fairly delicate, and a lighter touch helps you end up with tender meatballs rather than dense ones.
Step 2: Shape the Meatballs Evenly - Lightly dampen your hands with water before you start shaping. Ground chicken is naturally sticky, and that little bit of moisture makes this job much less frustrating. A number 20 scoop is great if you have one because it gives you evenly sized portions, but any spoon or small scoop will work. Portion the mixture and gently roll each piece into a ball. You should get about 22 meatballs. Keeping them close to the same size helps them finish cooking at roughly the same time.
Step 3: Prepare the Baking Dish - Pour 1 tablespoon of olive oil into the bottom of a casserole dish and spread it around so the surface is lightly coated. Arrange the meatballs in a single layer with a little room between each one. That space matters because it lets the hot air move around the meatballs and helps the outside develop a little golden color instead of simply steaming.
Step 4: Bake Until Tender and Golden - Place the casserole dish in the preheated oven and bake the meatballs for about 25 minutes. You are looking for lightly golden edges and fully cooked centers. Ground chicken should reach an internal temperature of 165°F. If you have an instant read thermometer, checking one of the meatballs near the center of the dish is the easiest way to know they are ready without cutting several of them open.
Step 5: Make the Pesto Olive Oil Drizzle - While the meatballs finish baking, stir the remaining 3 tablespoons of olive oil together with 2 tablespoons of basil pesto. Keep stirring until the pesto loosens into a smooth, spoonable mixture. It takes less than a minute, but this little finishing step makes a noticeable difference. The oil carries the basil and garlic over the surface of every hot meatball and gives them that glossy, just finished look.
Step 6: Drizzle the Hot Meatballs - Take the casserole dish out of the oven and immediately spoon the pesto olive oil mixture over the meatballs. Doing this while they are still hot helps the drizzle settle into the browned surfaces instead of simply sitting on top. I like to turn a few meatballs gently with a spoon so some of that pesto oil reaches the bottom of the dish too. Those little green pools around the edges are especially good spooned over pasta or rice.
Step 7: Garnish and Serve - Scatter fresh basil over the meatballs and add the pine nuts if you are using them. Serve everything while it is hot, preferably with something that can catch the pesto oil from the bottom of the dish. Pasta is the obvious choice, but rice, mashed potatoes, crusty bread, or roasted vegetables all work. Put the dish on the table family style and dinner is ready.