Lightly coat the bottom of a 5-quarter or larger slow cooker with nonstick spray. In a large mixing bowl, place the beef, panko, milk, parsley, Parmesan, Italian seasoning, salt, pepper, onion powder, garlic powder, and eggs. With a fork, break up the meat and stir the ingredients together until evenly combined.
Gently form the mixture into 2-inch meatballs, being careful not to compact the meat. If the mixture is sticking to your hands, wet them slightly. Arrange them in a single layer in the bottom of the slow cooker. You’ll have about 12 meatballs total.
Pour the pasta sauce over the top. Sprinkle evenly with the garlic and red pepper flakes.
Cover the slow cooker and cook the meatballs on HIGH for 2 to 2 1/2 hours, until the meatballs are cooked through (slice one in half to check). With a spoon, gently turn the meatballs to coat them in the sauce and distribute the garlic and red pepper flakes.
Sprinkle additional Parmesan and parsley on top, to taste. Serve as desired.
TO STORE: Refrigerate meatballs in an airtight storage container for up to 4 days.
TO REHEAT: Rewarm leftovers in a skillet on the stovetop over medium-low heat or in the microwave.
TO FREEZE: Freeze meatballs with the sauce in an airtight, freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.