In a blender or food processor, blend garlic, yogurt, mayonnaise, parsley, tarragon, chives, lemon zest, lemon juice, fish sauce, ½ tsp. salt, and a few grinds of pepper until smooth. Season with more salt and pepper, if needed.
Transfer ¼ cup sauce to a large bowl (for the meatballs).
Transfer remaining sauce to a medium bowl and refrigerate until ready to use.
To large bowl with sauce, add egg, panko, salt, and a few grinds of pepper and stir to combine. Add chicken and gently mix to combine (do not overmix).
Refrigerate until mixture firms up, about 10 minutes.
Arrange a rack in center of oven; heat broiler. Lightly grease a baking sheet with cooking spray. Roll meat mixture into 20 balls and arrange on prepared sheet.
Broil meatballs, watching closely, until cooked through and browned on top, 6 to 8 minutes.
Divide orzo (if using) among plates. Top with meatballs, then drizzle with refrigerated reserved goddess sauce.
