Cook the spaghetti as per the packet instructions
Blanch and puree the spinach.(Blanch- Boil water.Add the spinach for 10 seconds and remove)
Add butter to a pan, let it melt at medium heat.
Add the maida once the butter has melted and saute
Add the milk and keep mixing with a spoon.Once the mixture seems smooth and the butter, maida and milk has combined add the spinach puree.
Now add the bell peppers and cook for 4-5 minutes till the sauce is bubbling.
Add the spaghetti and serve!