Heat oil in a wide pot over medium heat. Add the yellow onion and cook briefly until it just begins to sweat. Add the shiitake mushrooms and cook for 10 minutes, stirring regularly, until the mushrooms and onions just begin to turn golden brown.
Add the aromatics:
Add the garlic and jalapeño (if using) and cook for 1 minute.
Sizzle the curry paste:
Add the curry paste to the vegetables and use your spoon to lightly mash it into the hot skillet. Cook for 1 minute.
Simmer the chickpeas:
Pour the water into the paste and stir to incorporate. Bring to a boil and season liberally with salt. Add the brown sugar and the chickpeas. Reduce heat and simmer, uncovered, for 30 minutes until the broth reduces down. Taste and season again to your preferences.
Cook the greens:
Stir the spinach and cilantro into the broth and cook for 1-3 minutes.
Finish the green curry chickpeas:
Add the coconut cream and cook for an additional 5 minutes. Taste and season again to your preferences. Turn off the heat.
To serve:
Serve the green curry chickpeas with cooked jasmine rice. Garnish with a lime wedge and Thai basil, if desired. Enjoy!