While the quinoa is cooking, make the butter mushrooms. In the same small skillet that you used for the acorn squash butter, melt the butter over medium heat.
Add the mushrooms and stir to coat with butter. Cook mushrooms, stirring occasionally for 10-12 minutes or until tender. Add parsley and stir to combine.
To assemble, add quinoa over the acorn squash and add mushrooms on top.