First steam or boil the potatoes, carrots, baby corn and peas in a steamer or pressure cooker. drain and then chop them. keep aside.

Heat enough water in a pan with salt and a few drops of oil.
when the water comes to a boil, add the pasta and boil them till they are completely cooked.

Strain the pasta and rinse with water. drain and keep aside.
in a pan, melt the butter. add the onions and garlic and saute till the onions are softened.

Then add the mushrooms. stir and saute the mushrooms till the mushrooms are lightly browned from the sides.
the mushrooms will release their juices initially and after continuous sauteing, the juices will evaporate. there should be no moisture in the pan.

Keep on stirring in breaks while sauteing the mushrooms.
then add the chopped capsicum/bell pepper and saute for 10 to 12 minutes.
add the flour and saute for 4 to 5 minutes.
add the boiled vegetables and saute for a minute.

Pour milk in a gentle stream to the pan and keep on stirring. the flour will combine with the milk and you will see the sauce getting thickened slowly. season with salt, pepper and oregano or basil or your choice of herbs.

When the sauce stars to thicken and reaches to your desired consistency. add the pasta.
stir well so that the sauce coats the pasta. switch off the flame.
if the sauce becomes too thick or lumpy, add some hot water or milk and thin the sauce.
lastly add some grated cheese if required.
serve the vegetable pasta in white sauce hot with some toasted bread or baguette.