Mix the yogurt with the mustard, 1 tablespoon of olive oil, and half of the chopped mint. Season with salt and pepper. Chill in the refrigerator.
Whisk the remaining olive oil with the lemon juice and soy sauce. Season with salt and pepper. Brush the mixture onto the mushrooms.
Combine the ground lamb with the spices, half of the garlic, and the remaining chopped mint. Season with salt and pepper. Shape into 12 mini patties with wet hands.
Slice the zucchini into thin rounds.
Cook the mushrooms on a grill or griddle for 6 minutes, the lamb patties for 4 minutes, and the zucchini slices for 2 minutes.
Spread some yogurt sauce on half of the mushrooms.
Layer with zucchini slices, a lamb patty, and some onion rings.
Top with the remaining mushrooms to close the burgers. Sprinkle with a bit of garlic powder and serve.