Preheat oven to 190°C. Spray a large non-stick frying pan with oil and heat over medium-high heat. Cook chicken, in batches, for 2 minutes or until golden. Remove and set aside.
Spray pan with a little more oil and reduce heat to medium. Cook leek, stirring occasionally, for 3 minutes or until soft. Add garlic and mushrooms and cook for 3 minutes or until mushrooms are golden. Add flour and cook, stirring, for 1 minute.
Gradually add stock, stirring constantly. Stir in potato and bring to a simmer. Cook for 10 minutes, or until potato is tender and sauce has thickened. Stir through cooking cream and chicken, simmer for 1 minute more.
Spoon mixture into two 1 cup (250ml) capacity ovenproof ramekins or pie dishes. Working with one piece of filo at a time, cut into quarters. Scrunch each piece of filo and loosely place on top of one pie to cover filling. Repeat with remaining filo. Bake for 15-20 minutes or until golden brown.
Meanwhile, cook peas in a saucepan of boiling water for 3 minutes or until tender. Drain well, then return to saucepan. Mash with a potato masher or fork, keeping some texture. Serve