Rinse the skinless chicken drumsticks under cold water and pat them dry with paper towels to help the seasoning stick better.
In a mixing bowl, combine kosher salt, fresh ground pepper, garlic powder, and dried oregano. Toss the chicken drumsticks in the seasoning mixture until evenly coated.
Squeeze the juice of one fresh lemon over the seasoned chicken, coating all the drumsticks for fresh and zesty flavor.
Arrange the seasoned chicken drumsticks in the slow cooker in a single layer for even cooking.
Cover the slow cooker and cook on low for 6-7 hours (recommended for tenderness) or on high for 3-4 hours.
During the last 30 minutes of cooking, sprinkle the freshly grated feta cheese over the chicken to melt slightly and infuse flavor.
Once cooking is complete, carefully remove the chicken drumsticks, place on a serving platter, drizzle with remaining juices, and serve warm.