Line a large rimmed baking sheet with foil.
In a medium bowl stir together herbs, panko, ¼ cup water, the egg, garlic, 1 tsp. kosher salt, ½ tsp. black pepper, and the cumin until well combined. Let stand 10 minutes.
Preheat broiler with oven rack in middle position.
Add lamb and feta to panko mixture; stir or mix gently with your hands until just combined.
Shape lamb mixture into twenty 1 ½-inch balls (about 2 Tbsp. each). Arrange meatballs evenly spaced on the prepared baking sheet.
Broil meatballs until lightly browned and no longer pink in centers, 8 to 10 minutes.
If you like, serve with pita bread and tzatziki.
