1. Heat oil in a large pan. Saute onion and garlic until onion is translucent.
2. Add spices and salt and saute for another minute.
3. Add sweet potatoes and broth. Bring to a boil, then reduce heat to simmer for 10-15 minutes.
4. Add tempeh and simmer until tempeh is cooked through and potatoes are tender.
5. Remove from heat, season to taste, and stir in half of the yogurt.
6. Serve hot, garnished with remaining yogurt and pumpkin seeds.