Heat up your oil in a skillet and add in your onion. Cook over medium heat stirring for about 10 minutes until lightly browned. About half way through the cooking add in your curry paste.
Add in your sweet potato, ginger, garlic, chopped cilantro stems and serrano pepper. Cook for a 3-5 minutes. Once this has cooked for a bit add in your chickpeas and tomatoes.
Pour in your stock or water, cover and let cook for another 5 minutes approx.
Pour in your coconut milk. Let simmer for a few minutes more until the sweet potato is cooked through.
Add in your spinach and stir to wilt.
Serve sprinkled with cilantro. Garnish with lemon wedges, yogurt, sambal oelek and naan if desired.