Pre-cut all vegetables for the ground beef stir fry. Cut the peppers and carrots into thin strands. Slice the mushrooms. Finely cut the green onion.
Combine all of the ingredients for the sauce, set aside.
Heat 1 Tbsp oil in a large skillet. Cook ground beef in the skillet, breaking up the meat as it's cooked. Remove meat from skillet, set aside and cover.
Using the same skillet, add the mushrooms, carrots and peppers with additional 2 Tbsp oil. Cook until vegetables are tender.
Add ground beef back to the vegetables. Pour sauce over and mix well.
Cook an additional 3 minutes and remove from the heat.
Top with green onions and serve.