Heat olive oil over medium-high heat in a deep skillet. Add garlic and heat until fragrant, about 20 seconds. Stir in onions and a pinch of salt. Saute until tender, about 5-6 minutes, stirring frequently.
While the onions are sautéing, use a pair of kitchen scissors to carefully cut the whole peeled tomatoes. Pour can into the pan along with the tomato sauce. Season with salt and pepper to taste. Bring sauce to a boil then remove from heat; set aside.
To prepare the meatballs, place all of the ingredients in a medium bowl and use your hands to mix until evenly incorporated. Begin rolling meatballs using a small ice cream scoop and place inside your Crock-Pot slow cooker.
Cover the meatballs with the marinara sauce and place the lid on the Crock-Pot slow cooker. Heat on Low for 4 hours or High for 2 hours. Garnish with fresh basil before serving over pasta if you wish.
This makes four large portions of meatballs and sauce but you could easily feed up to six if serving over pasta. Nutrition facts do not include pasta.