Heat a heavy-duty fry pan or cast iron pan over med-high heat. Add the onion and sauté until translucent and golden, about 5-7 minutes. Add the garlic, ginger and lemongrass, sauté for another minute or two. Add the curry powder, mix into the onion mixture, cook for another minute.
Add the coconut milk. And the water to the empty can of coconut milk, swish it around the can and dump that water into the pan with the coconut milk, let it boil, add the lime juice, salt, and chilis. Let the sauce boil and reduce for about 6-7 minutes. Taste the sauce, add more salt, chilis or lime to taste. At this point, you can refrigerate the sauce and heat it back up when you are ready to use it.
Add the shrimp to the pan, let cook for 10 minutes or so, they should be pink and opaque.
Add the basil and spinach. Let the sauce thicken so that it coats the back of a spoon, about 3-4 minutes.
Transfer it all to a serving dish (or serve right from the pan) and garnish with chopped jalapeno, cilantro, green onion.
Serve with the cooked rice and lime wedges.