Start water for noodles.
Heat 1 tablespoon olive oil in a large skillet over medium heat. Add onion and cook until translucent. Add bison, mustard, salt, and pepper and cook until almost browned. Add mushrooms and cook until mushrooms are reduced by half, about 3 minutes.
Immediately before serving, add sour cream and heat. Overheating will cause the sour cream to separate.
Serve over hot parsley noodles.