Dice the onion and sauté it in a heated pan with a little oil for a few minutes. Add the lean ground beef and cook until browned. Stir in the tomato sauce and let it simmer for a short while.

Prepare two small glass containers or baking dishes. Spoon a layer of the beef mixture into the bottom of each dish. Place one lasagna sheet on top and spread a thin layer of Greek yogurt over it. Repeat the layering once more, then finish with a sprinkle of shredded mozzarella on top.

Bake in a preheated oven at 200°C (392°F) for about 30 minutes, or until the top is golden brown and bubbling.