In a large bowl combine the mince, ¾ of the onion, rice crumbs, egg, salt, pepper and half of the parsley. Use your hands to mix everything together and form them into 4 patties.
Heat the olive oil in a frying pan and place the patties in the pan. Cook the patties for 3-5 minutes on each side until they are cooked through.
Meanwhile, bring a saucepan of water to the boil and cook the sweet potato for around 10 minutes, or until they are tender.
Strain the potato from the water and whilst they are still warm stir the feta gently through the potato so that it melts and forms a creamy dressing. Season the potatoes with sea salt, pepper and remaining parsley.
To make the relish add the remaining onion and diced tomato to the pan that the rissoles were cooked in and sauté the tomatoes for a few minutes until they are tender. Season them with a little pepper.
Serve the rissoles topped with the relish and a side of sweet potato and salad leaves.