In a large bowl, mix together all meatball ingredients with a large spoon or spatula until just combined. Avoid overmixing.

Scoop a portion of the mixture (about 2 tablespoons) and roll it into a ball with your hands. Place it on a baking sheet lined with parchment paper. Repeat with remaining mixture until you have about 30–34 meatballs. Set aside.

Grease a 4-quart or larger slow cooker with nonstick spray or a drizzle of olive oil.

Add the onions, then pour one can of crushed tomatoes over the onions. Add the tomato paste and minced garlic, stirring gently to combine.

Heat a large skillet over medium-high heat. Add a tablespoon of olive oil and swirl to coat. Sear the meatballs in batches (about 6–8 at a time) for about 1 minute on each side until browned. Transfer the browned meatballs into the slow cooker.

Once all the meatballs are added, pour the remaining can of crushed tomatoes on top. Add crushed red pepper flakes and bay leaves.

Cover and cook on low for 6–7 hours, or on high for about 4 hours if you need it done quicker.

Remove and discard bay leaves before serving.

Serve warm with sauce over pasta, in a sub roll, or on their own. You can top with chopped basil, parsley, or fresh parmesan cheese if desired.

Store leftovers tightly covered in the refrigerator for up to 1 week. You can also freeze leftover meatballs for up to three months. Just thaw them overnight in the fridge before reheating.