Spaghetti Napolitan

Ingredients for Napolitan
(serves 2)

150g Spaghetti (5.29 oz)
1500ml Water (6.34 u.s. cup)
2 tsp Salt
1/2 Onion (120g/4.23 oz)
1 Garlic Clove

4 slices of Beef (100g/3.53 oz)
5 Button mushrooms
2 Bell Peppers

2 tbsp Olive Oil
3 tbsp Tomato Ketchup
3 tbsp Parmesan cheese (1 tbsp for topping)　

1/2 tbsp Butter
Parsley