Heat the oil in a saucepan over a medium heat, add the shallots and pancetta and cook, stirring frequently, for 6–8 minutes until golden. Add the chillies and tomatoes, partially cover the pan and simmer for 20 minutes until the sauce is thick and has reduced. Season with salt and pepper.
Meanwhile, cook the pasta in a large saucepan of salted boiling water according to the packet instructions until al dente.
To make the mollica, put the bread in a food processor and process to crumbs. Melt the butter in a frying pan over a medium-high heat, add the breadcrumbs and garlic and cook, stirring, until golden and crisp. (Don't let the crumbs burn, or the dish will be ruined!)
Drain the pasta and toss with the tomato sauce. Serve immediately with a scattering of the garlic crumbs, garnished with parsley sprigs.