Heat oil and butter in a frying pan, cook onion over a medium heat for 7 minutes, stirring occasionally. Add garlic and cook for a further 3 minutes, until golden and crisp.
Bring a large pan of water to the boil. Add pasta and cook for 5 minutes. Add asparagus and cook for a further 2 minutes, add peas and cook for further 2 minutes. Drain well.
Return pasta and vegetables to the pan, add most of the onion. Add gosts cheese, sea salt and black pepper, mix to combine. Serve topped with the remaining onions.