Use a small sharp knife to cut 3 slashes, about 4cm long and 1cm deep in each chicken breast.
Place the peppercorns, pepitas and orange rind in a mortar and pound with a pestle until a firm paste forms. Rub the mixture over both sides of the chicken.
Heat half the butter and 2 tablespoons of the oil in a large frying pan over medium heat. Add the chicken and cook for 3-4 minutes each side or until cooked through. Transfer to a plate and cover with foil to keep warm. Add wine to the pan and cook, stirring, for 1 miunute or until heated through. Add orange juice and sugar and cook, stirring occasionally, for 25 minutes or until sauce reduces to 1/2 cup. Remove from heat. Strain through a fine sieve into a heatproof jug.
Meanwhile cook potato in a saucepan of boiling water for 10 minutes or until tender. Drain, return to the pan with the garlic and use a potato masher or fork to mash until almost smooth. Add lemon juice and remaining butter and oil and stir with a wooden spoon until thick and creamy. Season with salt and pepper.
Divide the mash amongst serving plates. Top with chicken and drizzle wiwth glaze. Serve with beans and brussel sprouts.