Into a pan, add and heat Olive Oil (2 tablespoon). Add Boneless, Skinless Chicken Thigh (1 pound), cut into 1/2-inch pieces. Season with Kosher Salt (1/2 teaspoon) and Ground Black Pepper (1/2 teaspoon).
Add Yellow Onion (1). Stir to combine. Cook for about 5 minutes, until chicken is no longer pink.
Into a pot, melt Butter (1 stick). Add Garlic (1 clove). Cook for 30 seconds.
Add Heavy Cream (1 1/2 cup). Whisk to combine over a medium heat, then bring to a soft boil.
Add Colby & Monterey Jack Cheese (1/2 cup). Stir to combine.
Season with Salt (1/4 teaspoon), Ground Black Pepper (1/2 teaspoon), and Dried Parsley (1 tablespoon). Mix to combine, then remove the pot from the heat.
Combine the Fettuccine (10 ounce), sauce, and chicken. Toss to incorporate well.