Cut the sweet potatoes into cubes, then finely slice the onion & garlic.
Heat 1 Tbsp olive oil in a large frying pan over medium heat. Cook the sweet potatoes, stirring, until tender for about 10 minutes. Transfer to a plate.
Heat the remaining oil. Gently sauté the onion and garlic. Put the sweet potatoes back and add the curry powder. Cook for 1 minute, then add ½ cup of water. Cook, until the water evaporates and potatoes start to brown (for about 10 minutes).
Add the spinach and cook, under cover, for 2 minutes until it wilts. Season with salt and ground pepper.
Serve with some lemon or lime juice squeezed over it.