Pre heat the oven to 180°C
Sauté the chopped onions in a large pan sprayed with some low calorie cooking spray. Cook until they start to soften
Stir in the Henderson's Relish, red wine vinegar, and thyme, then add the made up beef stock. Bring to the boil and allow to simmer for 10 minutes. The liquid should reduce by about half
Stir in the peas. Add the cornflour slurry and bring to a bubble until thickened.
Remove from the oven and serve