Steam cauliflower until tender crisp. About 5 mins in a steaming basket over simmering water, or you could use the microwave.Preheat oven to 425.In a large skillet, heat 2 tablespoons olive oil. Add the onions, cinnamon and oregano. Saute until the onions are tender, about 7 minutes. Add the garlic and tomatoes and simmer for another 5 minutes or so, until some of the liquid from the tomatoes is evaporated.Dump the onions and tomato mixture into a medium sized casserole dish, layer cauliflower on top, pushing some of the florets into the tomatoes. Sprinkle with Parmesan cheese and walnuts. Drizzle the remaining olive oil on top, if desired, and place in the oven for 15-20 minutes. Tomatoes will begin to bubble and cheese will melt become lightly toasted. You could even turn on the broiler for a minute or two to get a nice browning on top -- just watch the walnuts. They will burn quickly.Remove from oven, sprinkle with fresh parsley and serve.