Heat oil in a large pan over medium heat and stir in onions. Cook 2 minutes till transparent then add garlic (and pepper flakes). Cook, stirring for 1 minute, then add tomato paste (and fresh chillies) and cook for 1 more minute.
Stir in and break up tomatoes and cook for 15 minutes until sauce thickens, stirring often. Stir in vinegar (lemon juice), fresh aromatics and salt and pepper.
Traditionally served mixed in with penne or other ridged tubular pasta, topped with parmesan and fresh parsley.