Heat oil in a 6-quart pressure cooker over medium-high heat. Add onions, ginger, garlic, and 1 teaspoon salt. Cook, stirring occasionally, until onions are translucent, about 3 minutes. Add cinnamon stick, cumin, coriander, turmeric, and cardamom. Cook, stirring, until spices are fragrant, about 30 seconds. Add tomato paste and cook, stirring, 15 seconds more.
Add lamb, potatoes, and broth. Season with salt. Secure pressure-cooker lid and bring to high pressure over high heat. Reduce heat to medium to maintain high pressure. Cook 24 minutes; remove from heat. Vent pressure, then remove lid. Stir in spinach. Season with salt and serve with accompaniments.
