Combine the buttermilk, Worcestershire, dry mustard, and cayenne in a shallow nonreactive baking dish. Stir in the onion and garlic and add the turkey cutlets, turning to coat. Cover and refrigerate for at least 4 hours or overnight.
Preheat the oven to 350°. Spread the bread crumbs on a baking sheet and toast for about 5 minutes, until lightly browned. Transfer to a plate and season with salt and pepper.
Drain the turkey cutlets and discard the marinade. Coat the cutlets with the seasoned bread crumbs, shaking off the excess. Coat a large nonstick skillet with olive oil cooking spray and warm over moderately high heat. Add one-third of the turkey cutlets and spray them lightly. Fry the cutlets, turning once, until cooked through and golden, about 3 minutes per side. Transfer to a platter, cover loosely with foil, and keep warm. Wipe out the skillet and repeat the process with more olive oil spray and the remaining turkey cutlets.
Transfer the turkey to warmed plates. Spoon the Three-Mushroom Gravy on top and serve with the spaetzle and roasted beets.
Wine Recommendation: This dish could be matched with a light, fruity red, such as Beaujolais, but a rich, round California Chardonnay, such as the 1992 Simi or Silverado Limited Reserve, has enough depth to match the rich savory flavors of the cutlets and spaetzle with gravy.
Notes: ONE SERVING: Calories 234 kcal, Protein 34 gm, Carbohydrate 17 gm, Cholesterol 72 mg, Total Fat 7 gm, Saturated Fat 1 gm