Heat oil in a large heavy-based saucepan over medium heat.
Add onions and toss to coat in oil, Cover.
Cook, stirring occasionally, for 10 minutes or until softened.
Remove lid. Add beer. Stir to coat. Cook, stirring occasionally, for 20-25 minutes or until golden.
Meanwhile, spray a large frying pan with oil. Heat over medium heat.
Add sausages. cook, turning often, for 12 minutes or until cooked through.
Divide sauerkraut, onion and sausages between hot dog rolls.
Serve with mustard.