Boil water in a large pot, add pasta and cook according to package instructions until al dente, then drain and set aside.

In a large skillet, heat olive oil over medium heat.

Add chopped onion to the skillet, sauté for about 5 minutes until translucent.

Stir in sliced mushrooms, cook for another 5-7 minutes until browned and tender.

Add minced garlic, sauté for an additional minute.

Sprinkle flour over mushroom mixture and stir well.

Pour in vegetable broth, soy sauce, and Dijon mustard; bring to a simmer and cook for about 5 minutes to thicken.

Remove skillet from heat and stir in sour cream until smooth.