Step 1Preheat oven to 200°C. Boil, steam or microwave potatoes for 10–12 minutes, or until tender. Cool slightly, then roughly mash.
Step 2Meanwhile, place a large non-stick frying pan over a medium heat and spray with olive oil. Add leek and cook for 2 minutes, or until softened.
Step 3Add frozen peas, corn and carrots, fish and mustard to the pan. Reserve 2 tablespoons of evaporated milk; pour the rest into pan and stir. Mix reserved milk with cornflour to form a thin paste. Slowly add this to the pan, stirring for 10 minutes, or until fish and vegetables are cooked through and sauce has slightly thickened. Add lemon juice and cracked black pepper to taste.
Step 4Divide fish mixture among 4 x 2-cup capacity ramekins, spray with a little olive oil, and top with mashed potato and grated parmesan.
Step 5Bake in oven for 10–15 minutes or until golden. Serve the fish pies with mixed salad leaves.