Heat the olive oil in a large saucepan on a medium heat, add the mince and the beef stock cube and brown the mince.
Dice the onion, and add to the mince.
Slice the mushrooms and peppers finely, and add to the saucepan. Cook until softened.
Mix in the tomato puree and oregano.
Add the two tins of tomato puree and simmer on a low heat for roughly 30 minutes.
Cook the pasta as per packet instructions and drain loosely. ( I prefer not to use a colander, so there is a little water still left in the bottom of the pan).
Add to the sauce and mix well, so all the spaghetti strands are coated.