Slow-cooked Meatball Marinara

1 large onion, diced  

40g breadcrumbs  

Leaves from 1 sprig of fresh thyme  

Salt and freshly ground black pepper   

2 eggs, beaten  

Olive oil, for frying 

For the sauce : 

150g smoked bacon lardons  

1 fresh red chilli, deseeded and diced  

500g tomato passata  

200g plum tomatoes (½ a tin)  

1 tablespoon paprika  

1 tablespoon garlic powder  

leaves from 1 sprig of fresh thyme  

To serve: 

4 baguettes or soft rolls  

Grated mozzarella cheese  

Handful flat-leaf parsley leaves, finely chopped  

Burger sauce