Cook diced onion in oil over medium heat for 8 to 10 minutes until soft and lightly golden. Do not rush on high heat.
Add garlic and ginger. Cook 90 seconds. Add tomato paste, stir and cook 1 minute until darkened slightly.
Add all spices. Stir constantly for 60 seconds to bloom in the residual oil.
Pour in diced tomatoes, coconut milk, broth, and salt. Add sweet potato cubes. Bring to a simmer, then cover partially and cook over medium-low for 18 to 22 minutes until sweet potato is tender.
Stir in chickpeas. Cook uncovered 5 more minutes. Taste and adjust salt and cayenne. Squeeze in half a lime.
Serve over basmati rice or with naan. Top with fresh cilantro and lime wedges.