Method:

1. In a pan - heat butter when it starts to melt add onion and fry till slightly golden then add carrots and saute till raw smell leaves.
2. Now add maida and give a quick saute then add remaining 1/2 tbsp butter.Now add milk and keep stirring. Keep stirring until the mixture becomes slight thick and creamy.Cook in low flame. Add required salt.
3. Once the sauce is thick in spreadable consistency add coriander and mint leaves, then oregano and pepper powder.Give a quick mix and switch off.Set aside to cool.Toast bread with ghee till both the sides turn golden brown.
4. Apply the prepared white sauce on one side of a bread and seal it with another bread.Cut into triangles and serve hot.
5. Another alternate method is apply the sauce,close with another bread and toast it.

My Notes:

You can add any vegetable of your choice.Capsicum,cabbage ,peas are few of my suggestions.
Oregano and pepper powder gives a great flavour.
I skipped green chillies and added pepper powder instead.
You can either toast and make sandwich and use sandwich maker.
I used white bread, you can use wheat or multigrain bread too.
I cut each them into small traingles to make serving for kids easier and they will love it too.
Just toast it till golden brown thats enough.
Make sure you cool down white sauce before you apply it.
The white sauce thickens with time so switch it off accordingly.
I haven't added cheese, if you want add 2 tbsp of grated cheese after the milk starts thickening.
After applying the white sauce, serve immediately else the sandwich will become soggy if resting time is given.