Cook the garlic & ginger: in a large, deep skillet over medium heat, add the oil. Once hot, cook the garlic and ginger for about 1 minute, until fragrant.
Add the curry paste: stir in the curry paste and cook for 1 minute more.
Simmer: add the coconut milk, sweet potatoes, chickpeas, soy sauce, and ½ cup water. Season with salt & pepper to taste. Bring the pan to a boil and then turn the heat down and simmer, covered and stirring occasionally, for 15 minutes. Potatoes should be tender. For a thicker curry, simmer 5 minutes more, uncovered.
Add the spinach & lemon: stir in the spinach and cook until barely wilted. Remove from the heat and stir in lemon juice.
Serve: optionally, serve with a side of white rice and topped with chopped peanuts & cilantro.