Place the mince in a bowl and add egg, olive oil, onion and the sachet contents.
Scrub the sweet potatoes then, without peeling them, grate using a cheese grater.
Stir into the mince mixture.
Line a loaf tin with baking paper and press the mixture into the tin.
Cover with foil and bake in a preheated oven at 180°C for 1 hour, then remove the foil.
Sprinkle with cheese and arrange sliced tomato on top then return to the oven and bake uncovered for a further 30 min.
Cut into thick slices.