Cook the spaghetti according to the instructions. Reserve a few tbsp of the pasta water in a separate bowl, and then drain the spaghetti. Leave in the colander.
Spray the saucepan with plenty of low calorie cooking spray. On a low heat, stir in the Bovril. If you like your pasta particularly tangy, then add a little extra more Bovril at this point to suit your taste.
Stir the pasta into the Bovril until the spaghetti is coated in the sauce. If you want a looser sauce, then mix in a couple of tbsp of the pasta water that you set aside earlier.
Serve with some freshly ground black pepper and some grated parmesan (optional).