This is a dish my Nonna used to make me every time I stayed overnight at her house. This was the Italian version of Mac-n-Cheese with bacon. I decided to add chicken when re-writing the recipe. The sauce is amazing - you will love it.
Do ahead: Make the Asiago sauce. In a medium saucepan, heat the heavy cream until it just starts to bubble, then whisk in the chicken bouillon powder and the shredded cheese. Blend 1/4 cup water and the cornstarch together then whisk into the cream sauce. Let the mixture thicken (must come to a low simmer), then remove from the heat and set aside, or let cool and refrigerate, covered, until ready to use. Bring the sauce back up to temperature very carefully by whisking frequently, until it just simmers for about 1 minute.
In a large skillet, melt the butter and saute the red onion, pancetta, and garlic. Let simmer until the vegetables are just softened. Add the green onions, grilled chicken, and the cooked pasta. Add the heavy cream to the pan, then add the Asiago sauce. Stir frequently to blend all the ingredients.
Pour the creamy pasta into warmed bowled and garnish with the chopped parsley.
Note: Substitute 4oz of regular bacon if you can't find pancetta; dice it and cook it before adding to the pasta sauce.