Whisk the yogurt and mustard in a bowl until smooth; set aside.
Pulse the bread in a food processor until finely ground. Transfer to a shallow dish and add the marjoram, and salt and pepper to taste. In another shallow dish, season the flour with the paprika and nutmeg. Beat the eggs in a third dish. Season the chicken with salt and pepper.
Dredge each cutlet in the flour, shaking off the excess. Dip in the eggs and then in the breadcrumbs, pressing to coat both sides. Place on parchment paper until ready to fry.
Heat 1/8 inch of vegetable oil in a large skillet over medium-high heat until hot. Add 2 cutlets, gently swirling the skillet so the oil washes over them, and cook until golden brown, about 3 minutes per side. Transfer to a paper-towel-lined plate and season with salt. Repeat with the remaining chicken, adjusting the heat as needed. Serve the schnitzel with the mustard sauce and applesauce, if desired.