Bring a steamer pot of hot tap water to the boil. Spray a baking dish with oil spray.
Make potato top
Peel 600 g potatoes and 1 parsnip and cut them into small chunks. Cook potato and parsnip in the steamer pot of boiling water for 12-15 minutes, or until tender. Transfer to a large bowl and add 1 tbsp olive oil and ¼ cup milk, season with salt and pepper and mash until smooth. Reserve the steamer pot with water.
Prep filling
While the potatoes are cooking, peel and finely dice or grate 1 carrot. Grate 1 zucchini. Slice 1 leek in half lengthways, then thinly slice. Pat 600 g fish fillets dry and dice into bite-sized pieces.
Cook filling
Heat 1 tbsp olive oil in a large frypan on medium-high heat. Cook carrot, zucchini, leek and fish for about 6 minutes, until tender. Add 1 cube chicken stock and ½ cup milk and cook for 2-3 minutes, until veggies are soft and the fish starts to fall apart. Remove from heat and stir through ½ cup sour cream. Season to taste with salt and pepper.
Cook pie
Preheat grill to medium-high. Transfer the filling to the prepared baking dish and top with dollops of mashedpotato. Grate over 50 g cheese and grill for 5 minutes or until the cheese is melted and golden.
Cook greens
Meanwhile, bring the reserved steamer pot of water back to a boil - add more hot tap water if needed. Add 1 cup frozen peas and1 cup frozen beans to the steamer pot of boiling water and cook for 4 minutes, until tender. Season to taste with salt and pepper.
To serve
Divide the creamy fish and leek pie with cheesy potato top between plates and serve with the steamed greens on the side.