Before cooking, wash your hands and put on an apron. Weigh or measure all the ingredients. Ask a grown-up to preheat the oven to 210C/415F/Gas 7. Oil an ovenproof dish.
Put the tomatoes into a cup and add a pinch of chilli flakes if you like things spicy. Stir with a fork and put to one side to use later.
In a bowl, mix the ricotta and black pepper together with a fork. Using scissors (ask a grown-up to help you), cut up the mint and spinach leaves into smaller pieces and add them to the cheese in the bowl. Mix until well combined.
Fold the lasagne sheet in half, matching the short sides. Gently run your fingers over the fold to help the pasta break into two pieces. Spread the cheese mixture on top of both pieces of lasagna, then roll them up into tubes, starting at the short edge.
Pour enough of the chopped tomato and chilli mixture into the ovenproof dish to cover the bottom. Place the rolled-up lasagne tubes into the dish and pour over the rest of the chopped tomatoes. Top with a sprinkling of grated cheese. Put the dish on the baking tray and ask a grown-up to cook it for 15-20 minutes. Serve with a green salad.