Preheat the oven to 220C/425F/Gas 7.
To make the ratatouille, heat the oil in a pan and sauté the peppers and onion for a few minutes, to soften. Stir in the potato and heat for another 1-2 minutes. Transfer to the oven and roast for 10-12 minutes.
For the steak, mix the chives, onion, parsley and Stilton together.
Make a slit along the steak to make a pocket. Stuff the mixture into the steak and then sear in a hot pan.
Drizzle with oil and fry in a hot pan for two minutes on each side. Transfer to the oven and cook for 4-5 minutes, or according to personal taste.
To serve, remove the roast vegetables from the oven and stir in the parsley. Transfer to a serving plate and serve the stuffed steak alongside.