Drain and rinse the pasta. Then get as much moisture out of them by drying on a towel.
Let the noodles sit while you prepare the cheese sauce.
In a small pot add the milk, flour, mustard, salt and pepper. Whisk it over medium heat until it warms. Add the cheese and keep whisking until it melts in.
Lower the cheese sauce to a simmer and start the noodles.
Heat a non-stick skillet over medium-high and spray with cooking spray. Add the noodles and toss, separating them so they can dry out a bit.
Add the ham and frozen peas and toss around mixing everything until the peas defrost and the ham warms, about 2 minutes.
Add the cheese sauce. Use a rubber scraper to make sure to get as much as possible to transfer to the skillet.
Toss everything together cooking for another minute or two. The noodles have a tendency to glob together; just keep separating them and mixing in the rest of the ingredients.