Add ground beef and onion to a large skillet and heat over medium high heat, stirring frequently until beef is browned. Drain grease from pan.
Return pan to stove and add cabbage.
Season with salt and pepper. Mix well and cover. Continue to heat over medium heat, stirring occasionally until cabbage has softened, about 10 minutes. Remove from heat and set aside to cool.
Flatten each roll to about a 4" circle.
Using a 2 tablespoon portion scoop, scoop filling into the center of the roll.
Bring up the sides and pinch together firmly. Repeat until all rolls are filled.
Heat about 1" of vegetable oil in a skillet over medium heat. Pinch the seams of the rolls together one more time and, working in batches, fry the bierocks until golden brown on each side.
Drain on paper towels and serve hot.