Toss squash with 1 Tbsp. olive oil and season with salt and pepper. Roast for 12 minutes, flip and continue cooking an additional 10-12 minutes. Remove and set aside.
In a large saucepan over medium heat, melt butter. When butter is bubbling, add buckwheat groats and toast, stirring continuously for about 5 minutes.
When groats are toasted, add 2 cups water and bring to a boil. Reduce to a simmer, cover and cook undisturbed for 10 minutes. Remove from heat and fluff with fork. Set aside.
In a large skillet over medium-high heat, warm 1 tbs olive oil until shimmering. When hot, add mushrooms, season with salt and pepper and cook until browned, about 5 minutes.
Add butternut squash and buckwheat groats, tossing to combine.
Add parsley leaves, season with salt and pepper and continue cooking until warmed through, about 3 minutes
