Cook the rigatoni according to directions, then drain and set aside.
Spray a large sauce pan with cooking oil and sauté the mushrooms for about 10 minutes (or until browned).
Remove the mushrooms from the pan and set aside.
Cook the sausage and the onion flakes in the same pan for about 12-15 minutes (or until fully cooked).
Remove the sausage from the pan and set aside.
Melt the butter over medium-high heat.
Add in the almond flour and whisk until a paste is formed.
Add in the milk, garlic powder, and salt/pepper.
Bring to a simmer and whisk continuously until the creamy sauce begins to thicken (about 7-10 minutes).
Remove from heat and add the rigatoni, mushrooms, and sausage back into the pan.
Mix everything together, serve, and enjoy!