Preheat the oven to 200°C/gas mark 6. Line a baking tray with baking parchment and set aside. Arrange the sweet potato wedges on another baking tray and drizzle over the oil. Toss to coat.
In a shallow dish, mix the breadcrumbs with the grated parmesan and lemon zest, then season with freshly ground black pepper. Put the beaten egg in a separate shallow dish.
Dip the chicken steaks into the egg, then press into the breadcrumb mixture to coat evenly on both sides. Put on the lined baking tray.
Bake the chicken on the middle shelf of the oven and the sweet potato wedges on the top shelf for 20-25 minutes until the chicken is cooked through with no pink remaining and the wedges are tender and golden.
About 5 minutes before the end of cooking time, bring a pan of water to the boil. Add the beans and cook for 5 minutes, adding the petits pois for the final 2 minutes. Drain the veg and serve with the chicken schnitzel and sweet potato wedges.