Cook the quinoa according to the instruction on the package. Once cooked, season with salt and pepper to taste and toss with pistachios. Cover with a lid to keep warm.
Heat the oil in a non-stick pan over medium high heat. Sauté the mushrooms until golden brown and soft. Add in the sliced steak and garlic. Brown the beef slices well. Then add in the snow peas and sauté for 2-3 minutes more. Season with salt and pepper then set the contents of the pan aside in a bowl.
Add the broth, soy sauce, and rice wine vinegar to the pan. Lower the heat to medium and bring to a simmer. Slowly stir in the cornstarch/water mixture. Once the liquid gets very thick, remove from the heat.
Toss the beef and vegetables with the sauce to coat well.