Arrange a rack in the upper third of the oven and heat the oven to 425°F. Line a rimmed baking sheet with aluminum foil if desired. Coat the foil or baking sheet with cooking spray.

Stir 2 ½ ounces grated Parmesan cheese (about ⅔ cup), ½ cup finely chopped fresh parsley leaves, ½ cup panko breadcrumbs, 2 finely grated garlic cloves, 1 large egg, 1 tablespoon fish sauce, 2 teaspoons Worcestershire sauce, 1 ½ teaspoons Dijon mustard, the finely grated zest of 1 medium lemon, ½ teaspoon kosher salt, and ¼ teaspoon black pepper together in a large bowl.

Add 1 ½ pounds ground chicken and mix until evenly combined; do not overmix or the meatballs will be tough. Scoop out the mixture in heaping 2-tablespoon portions (about 26) and roll between damp hands until a smooth ball forms. Place on the baking sheet, spacing them evenly apart.

Roast until cooked through and an instant-read thermometer inserted in the center of a meatball registers at least 165°F, 12 to 15 minutes. Switch the oven to broil and broil until golden-brown on top, 2 to 3 minutes more. When the meatballs have 5 minutes of cooking time left, make the sauce.

Melt 1 tablespoon of the cold unsalted butter in a medium skillet over medium-high heat. Add 2 sliced garlic cloves and cook, stirring frequently, until fragrant and lightly browned, about 2 minutes. Remove the skillet from the heat. Whisk in the remaining 4 tablespoons cold unsalted butter and ¼ cup lemon juice until the butter is just melted. Taste and season with kosher salt as needed.

Add the meatballs to the skillet and toss to coat. Garnish with more black pepper, finely chopped parsley leaves, and grated Parmesan cheese.