1. In a pan pour water. Add oil and salt. Bring it to boil. Put in the spaghetti and cook for around 5 minutes or till done. Drain in a colander and pour cold water over it. Set aside.
2. Preheat the oven to 150 degrees C.
3. Grease a baking dish with butter. Set aside.
4. In a pan, melt butter. Put the onions and capsicum. Saute for around 2 minutes or till the onions is soft and translucent. Transfer around ½ cup worth of the onion-capsicum mixture into a bowl.
5. To the remaining onion capsicum mixture pour the tomato puree. Season with salt, pepper, oregano, chilli flakes and sugar. Stir well to mix and bring it to boil. Add the tomato sauce and stir well.
6. Put in the cooked spaghetti and mix well. Pour the fresh cream, stir and bring it back to boil. Cook for another 2 minutes.
7. Pour this into the greased baking dish. Sprinkle retained onion-capsicum mixture on top followed by the cheese. Bake for around 20 minutes.
8. In a serving plate or bowl, serve the spaghetti hot.