In a large bowl, combine ground beef, panko, egg, 3 cloves of minced garlic, parsley, parmesan cheese, salt, and pepper.
Mix by hand until just combined and form into approximately 16 one-inch meatballs.
Heat a large skillet over medium-high heat and add a light coating of oil.
Add meatballs to the skillet and sear for 8-10 minutes, turning occasionally until browned on all sides and cooked through.
Remove meatballs from the skillet and transfer to a plate.
Reduce heat to medium and add the butter to the skillet, scraping up any browned bits.
Add the remaining 3 cloves of minced garlic and red pepper flakes to the melted butter and sauté for 1 minute until fragrant.
Stir in the lemon juice to emulsify the sauce.
Return the meatballs to the skillet and toss continuously for 2 minutes to coat them in the garlic butter.
Garnish with fresh parsley and serve immediately.