Heat the oil in a large saucepan and add the onion. Cook for 2-3 minutes until beginning to soften, then add the peppers. Cook for another 3-4 minutes until the peppers are just becoming tender.
Add the chilli powder, cumin and paprika to the pan and stir through, cooking for 1 minute. Put the mince in the pan and move around, breaking up with a wooden spoon. Cook for 3-4 minutes until brown all over.
Pour in the passata and stock. Bring to a gentle simmer and cook for 30 minutes.
Put the chocolate in a heatproof bowl and heat in the microwave for around 30 seconds until melted. Add this to the chilli along with the beans. Alternatively, you can add the pieces of chocolate straight to the chilli. Stir to combine, then simmer for another 15 minutes until the mixture has thickened slightly.
Meanwhile, cook the sausages according to the instructions on the packet. Put the sausages in the rolls along with spoonfuls of the chilli. Serve with the ketchup, mustard and sliced red chilli and freeze any leftover chocolate chilli to enjoy later in the week.