Cook the chicken - you can broil or grill for 10-12 minutes, or use my instructions in my post for cooking in the Instant Pot or slow cooker. Slice or cube the chicken and set aside to keep warm.
Slice the Colorado green chiles and remove the seeds using a spoon. Dice and set aside.
Cook pasta in a large pot according to the instructions on the package. Drain and set aside.
Combine the cornstarch and milk in a bowl and set aside.
Toast the walnuts with salt in a small pan over medium heat. Stir frequently to ensure they do not burn. Set aside.
Melt the butter and olive oil in a large saucepan over medium heat. Saute the garlic for about 3 minutes, watching closely so that it does not burn. Slowly stir in the cream or half and half and bring just to a boil. Reduce heat to medium low.
Add the cornstarch/milk mixture to the sauce in the pan and stir to thicken. Add the diced green chiles, chicken and salt. Heat through. Stir in the cooked pasta, walnuts and cheese.
Season with black pepper and serve!