1. If you’re using oatmeal, lightly toast it in a dry frying pan, stirring often, until lightly brown, for about 5 minutes.
2. Put the sweet potatoes into a pan of water, bring to the boil, then turn down the heat and simmer until tender, about 6 minutes.
3. Meanwhile, put all the remaining ingredients except the egg, feta and oats, into a mixing bowl and combine well.
4. Drain the sweet potatoes, mash them with a fork and add them to the mixing bowl along with the egg, then carefully stir in the feta. Form the mixture into 6 patties and press them into the toasted oatmeal (if using). Wrap each patty in a single sheet of foil. These can rest in the fridge for up to 5 hours.
5. Cook the foil-wrapped burgers on the barbecue for 10 minutes, turning over once. Put a parcel on each plate, open them up and serve.
Recipe courtesy of Waitrose