Boil pasta as per package directions. Once pasta is fully cooked, strain and pass it under cold running water so it doesn't stick. Keep it aside.
In a deep skillet, add oil. Once hot add flour and stir. Let it get slightly golden and let the raw smell go away.
Now add milk and water slowly and keep stirring it continuously using a whisk so there are no lumps in the sauce. Add sauce and black pepper. Keep cooking and stirring until the sauce starts to thicken a bit. Add cheese and keep mixing. Add salsa verde and keep mixing. Make sure sauce is a bit thicker but not too thick or as it sits it will dry out. Taste and adjust as per taste.
Add the already cooked pasta and mix. Serve.
Recipe by Naive Cook Cooks at https://www.naivecookcooks.com/30-mins-salsa-verde-mac-and-cheese/