Preheat oven to 190°C. Bring a medium pot of salted water to the boil.
Cook kumara and swede in pot of boiling water for 12–15 minutes, until very soft. Drain and mash with butter, and season to taste with salt and pepper.
While vegetables cook, prepare pie filling; heat oil in a large fry-pan on medium heat. Fry onion, garlic, carrot and courgette until soft, 3–4 minutes. Add beef mince and cook for 3–4 minutes until brown, breaking up with a wooden spoon. Add tomato paste, soy sauce, Worcestershire sauce and mustard, stir until combined. Sprinkle over flour, stir to combine and cook for 1–2 minutes then add beef stock, stir and simmer for 5–7 minutes until sauce has thickened. Season with salt and pepper.
Half fill 5 large individual ramekins (1 cup capacity) with filling or use one large pie dish. Spread mash over to cover, rough up the surface with a fork and sprinkle over cheese. Bake for 10 minutes, then increase to grill, for about 3 minutes, until topping is golden. Rest for 5 minutes.
Bring a medium pot of salted water to the boil. Cook peas and beans for 2–3 minutes until just tender, then drain.
To serve, place individual ramekins (or serve spoonfuls) of mince and cheese pie onto plates and sprinkle over parsley. Serve peas and beans on the side with a dollop of tomato sauce, if desired.