Prepare fries according to package directions.
Meanwhile, in large skillet over medium heat, cook and crumble ground beef until no longer pink; drain. Stir in tomatoes and seasoning mix; simmer 5 minutes.
Stir in cheese; reduce heat to medium-low. Continue cooking, stirring frequently, until cheese is melted.
Place fries on a serving platter. Top with chili cheese and onions. Serve immediately.