Cook pasta in boiling water for about 5 - 6 minutes, not quite al dente, it will finish cooking in the oven. Drain and set aside.
Add butter to a large skillet and place over medium heat. Stir in diced onions, cooking until onions just start to brown around the edges, about 3- 5 minutes.
Next, add in flour, stirring constantly, cooking about 2 minutes.
Pour in milk and chicken base, use a whisk to combine until sauce starts to thicken. Lower to simmer.
Add garlic, onion powder, thyme, salt and pepper, whisk to combine.
Next, add sour cream and 1 cup of mozzarella cheese, stir until cheese is melted.
Turn off the heat. Add cooked pasta and mix well.
Add diced chicken and 2/3 of the bacon. If you do not have an oven safe skillet, pour mixture into a baking dish.
Top with remaining cheese and remaining bacon.
Bake for 15 - 20 minutes or until mixture is bubbly around the edges and cheese is melted.
Garnish with chopped parsley.