Heat olive oil in a large saucepan over medium heat, add onion, garlic, parsley, oregano and chilli and sauté for 5 minutes or until soft. Add silverbeet stems and cook for another 7-10 minutes. Add silverbeet leaves and cook, stirring, for 5 minutes or until beginning to wilt. Add tomatoes, tomato paste and 1½ cups water, season with sea salt and stir to combine. Bring to the boil and simmer for 45-50 minutes or until silverbeet is tender and sauce is thick. Serve immediately.