Wash the thyme and rosemary sprigs. Pinch the leaves from the stems and discard the stems.
In a bowl, combine the yogurt, honey, mustard, garlic, thyme leaves, rosemary leaves, chili powder, and salt. Stir well. Taste and adjust salt if needed. If using very lean yogurt, stir in the olive oil.
Place the 6 chicken schnitzel in a dish. Pour the marinade over them, coating well. Cover and refrigerate for at least 3 hours or overnight for deeper flavor.
Remove the chicken from the marinade and drain well. Heat a grill to medium-high heat. Grill each schnitzel for 3-4 minutes per side until lightly browned and the internal temperature reaches 74°C (165°F).