Half fill a large saucepan with water and bring to the boil over a high heat. Cook the pasta in the boiling water for 10-15 minutes or until only just tender. Drain in a colander and spray with a little of the oil to stop it sticking, then return to the pan.
While the pasta is boiling, melt the butter in a large non-stick saucepan and gently cook the onion, celery, garlic and thyme for 5 minutes, or until the onion is well softened but not coloured, stirring regularly.
Sprinkle the flour over the sauteed onion and garlic and stir well. Slowly add the wine, then the stock, stirring continuously to avoid any lumps. Bring to a gentle simmer and cook for 5 minutes, stirring frequently.
Meanwhile, spray or brush a large non-stick frying pan or wok with oil and stir-fry the mushrooms for 3-4 minutes over a high heat until lightly browned.
Stir the mushrooms, cream, peas and milk and chicken into the sauce and cook for a further 2-3 minutes more, stirring until hot. Tip onto the drained pasta and toss well together. Transfer to a warmed, shallow flameproof lasagne dish.
Mix the breadcrumbs and Parmesan together and sprinkle over the top of the pasta. Cook under a preheated hot grill for 5-10 minutes or until golden brown.