Heat the oil in a large shallow casserole, skillet or frying pan over a medium low heat. Fry the onion for 6 to 8 minutes, until softened but not golden, stirring occasionally. Stir in the garlic and cook for 2 minutes, then turn the heat up to medium and pour in the wine. Bring to a simmer and cook for 1 to 2 minutes so that the alcohol evaporates.

Pour the stock into the casserole and stir in the lemon zest, juice and orzo. Season well with salt and freshly ground black pepper and cook for 4 minutes before nestling the salmon fillets in. Cook for 3 minutes, then add in the asparagus pieces, stirring gently to cover them. If it's starting to seem a bit dry, pour in a little water. Turn the salmon fillets over and cook for another 3 minutes, until the salmon is cooked through and the asparagus and orzo are tender.

Stir in the mascarpone breaking up the cooked salmon fillets into chunky flakes. Serve with the lemon wedges and garnish with grated parmesan and freshly ground black pepper.