Cook spaghetti according to package directions and mix with marinara, keep warm
Drizzle avocado oil into deep skillet until bottom is coated, and turn heat to medium-low
In a medium mixing bowl, add ground beef, onions, salt, and pepper, and mix together until combined
Roll about 1 tablespoon of mixture into a ball (there will be 16 balls total), and dredge in flour, repeat for rest of meatballs
Place the flour-coated meatballs into the skillet and cook until no longer pink inside and outside is crispy, turning every few minutes
Plate the spaghetti and meatballs and eat up!