Preheat oven to 180 degrees.
Mix cream, mustard, parsley, and salt/pepper in a medium bowl.
Pan fry asparagus and mushrooms in olive oil on high heat for 3-4 minutes. Then add spring onion and the capers to the pan and fry for a further minute.
Cut fish into serving size proportions and add to a casserole dish, along with the cooked vegetables, followed by the cream mixture. Mix to combine.
Cover dish and bake in the oven for 30 minutes.
Divide casserole into 4 bowls and serve with a garden salad.