Fry off your pork sausages, breaking up into little pieces as you go, until nicely browned. Add your onion, garlic, fennel, chilli, salt, pepper and sugar. Fry for a further 5 minutes until your onions are nicely translucent and your garlic and spices have cooked off (to remove raw flavour). Remove from heat.
Place a quarter of your meat mix into your slow cooker. Add 1/2 cup marinara sauce, some mozzarella, basil leaves and ricotta. Lay on a layer of lasagna sheets. Repeat until you have used all of your ingredients (apart from parmesan).