Heat a 10 inch sauté pan over medium high heat. To the hot pan, add the oil. When the oil is hot, add onions and garlic and cook until onions are translucent, about 2 minutes. Add mushrooms and cook for 1-2 minutes. Remove half of this onion and mushroom mixture and set aside to mix in at the last minute.
Add ground beef to the remaining vegetables, and break up the lumps. Add Worcestershire sauce, mustard, broth, salt and pepper.
Cover and cook until the beef and vegetables are cooked through, about 5 minutes
Meanwhile, using a vegetable peeler, peel the zucchini into long ribbons. Place ribbons in a microwave safe bowl, add 2 tablespoons water. Cover and steam for 2 minutes. Remove and toss with 1 tablespoon butter.
When the beef is done, remove lid, and turn down the heat to low. Slowly stir in sour cream a little at a time and allow the mixture to gently bubble and thicken. Add back the reserved onion and mushroom mixture and stir in.
Serve over zucchini ribbons
Buy ready made zucchini noodles or use shirataki noodles instead.
Riced cauliflower also makes a wonderful accompaniment to this dish.
Saute all of the onions, garlic, and mushrooms at the beginning, but remove half before adding the ground beef. This creates rich foundational flavors in the dish, and also bright, fresh top notes.
Steam the zucchini noodles while the beef is cooking
Toss the zucchini noodles with a touch of butter to give the noodles flavor and substance.
Stir in the sour cream only at the very end of cooking to prevent it from curdling or separating.