Preheat the oven to 375 degrees and line a baking sheet with parchment paper.
In a large bowl, combine the ground lamb, breadcrumbs, egg, onion, 2 cloves of the minced garlic, oregano, mint, feta, and a pinch of salt and pepper. Mix until just combined.
Divide the mixture into 8 equal portions and shape each into a small loaf. Place the loaves on the prepared baking sheet.
Bake for 25 minutes until the internal temperature reaches 160 degrees. Let the meatloaves cool completely before freezing in a single layer, then transfer to a freezer bag.
While the meatloaves bake, stir together the Greek yogurt, grated cucumber, remaining clove of minced garlic, dill, and lemon juice in a bowl to make the tzatziki. Season with salt and pepper, then cover and refrigerate.
Cook the orzo in boiling salted water according to package directions. Drain and set aside.
To serve, reheat the frozen meatloaves in a 350-degree oven for 15 minutes. Plate with warm orzo and a generous spoonful of tzatziki.