Preheat an oven to 220 degrees C. Line a 20x30cm baking dish with aluminium foil and spray with nonstick cooking spray.
Mix the egg and onion together in a mixing bowl. Add the tomato pasta sauce and beef mince then season with pepper, salt, Italian herbs and bread crumbs; combine until evenly blended. Place the mixture into the prepared pan and pat into an 20cm square.
Use a table knife or metal spatula to cut the square into 6 vertical strips, then cut the strips horizontally into 6 pieces each for a total of 36 pieces. Do not separate the pieces, just press through the meat to separate it.
Bake in the preheated oven until the meatballs are no longer pink in the center, 20 to 25 minutes. Drain off any grease and separate the meatballs with a knife to serve.