Put the olive oil or butter in a 10 to 12 inch cast iron skillet or casserole dish and brush evenly.
Add the diced onions to the skillet or casserole dish. Cut the breakfast sausage into fourths and place over the onions,
Set the Traeger to 225 degrees (turn super smoke on if that's an option for your Traeger model). Place the skillet or casserole dish on the grill grate for 1 to 1 1/2 hours.
Break the sausage apart with a spatula in the skillet or casserole dish. Pour the heavy cream over top and season with kosher salt, pepper, and crushed red pepper flakes.
Increase the Traeger temperature to 350 degrees. Keep the skillet or casserole dish with the gravy on the grill grate for 30 to 45 minutes, stirring a few times. It will bubble and thicken as it cooks.
Open the biscuits, separate, and place on a baking sheet. Place the baking sheet on the Traeger with the gravy during the last 12 to 15 minutes.