Upside-Down Rice with Cauliflower, Eggplant, and Lamb (Maqloubeh)

Ingredients

• 1 1⁄2 tbsp. whole black peppercorns
• 1 tbsp. coriander seeds
• 1 tbsp. cumin seeds
• 1 tbsp. green cardamom pods
• 1 tbsp. whole allspice
• 1 stick cinnamon
• 1 tsp. curry powder
• 1⁄2 tsp. freshly grated nutmeg
• 1 1⁄2 lb. boneless lamb shoulder, cut into 1" pieces
• Kosher salt and freshly ground black pepper, to taste
• 1 large eggplant, peeled and cut into 1" pieces
• 1 small head cauliflower, cut into medium florets
• 2 cups basmati rice
• 2 tbsp. unsalted butter, melted
• 2 cloves garlic, minced
• 1 large white onion, minced
• 2 medium vine ripe tomatoes, cored and sliced 1/4" thick
• Greek yogurt, for serving