In a small bow, whisk together the evaporated milk and cornstarch. Add in the tuna and frozen veggies and mix well. Pour over the egg noodles in the inner dish and give a quick stir.
Top with the butter and then close the lid on the HeatsBox and plug it in.
Choose these settings from the app: 185 degrees F (85 degrees C), Large portion, Cooking, 45 minutes.