Bring a large pot of lightly salted water to a boil. Add tomatoes and cook for 10 minutes. Drain and rinse with cold water. Remove skins and return tomatoes to the pot and mash them. Stir in tomato paste and 2 cups (500ml) water. Cover and simmer on low heat.
Meanwhile, melt butter in a large frypan over medium heat. Saute garlic and bay leaves for 1 minute then stir in onions; saute until onions are translucent. Stir in zucchini, green and red capsicum and mushrooms. Slowly cook and stir for 5 to 7 minutes.
Stir vegetables into tomato sauce and add oregano, Italian herbs, chilli powder and brown sugar. Simmer over low heat for 6 to 8 hours. Stir in the ricotta cheese 10 minutes before serving.