Combine flour and oats in a bowl. Rub in small bits of the softened butter until mixture resembles coarse breadcrumbs. Toss cheese through and add a little water to make a soft dough. Stand for 30 minutes, covered, before using.
To make filling, toss together rice, salmon avocados, sour cream, onion, tomatoes, beaten eggs, lemon juice and parsley.
Grease a pie dish or oval casserole dish.
Roll out just over half of pastry on floured surface and fit into bottom of pie dish. Spoon in filling. Roll out remaining pastry to cover top of pie and seal edges together well by pinching them against the sides of the pie dish. Put a small slit in the middle of the pastry to allow steam to escape during cooking.
Glaze the top with a little milk and bake in a moderate oven 180°C (350°F) for 30 minutes.
Note: This pastry is rolled a little thicker than normal shortcrust pastry, as you will notice when rolling it out to fit the pie or casserole dish.
Hint: Roll the pastry on a sheet of floured foil and use that to transport it.