Add the coconut milk and vegetable broth and bring to a boil. Reduce heat to a light simmer, cook uncovered for 15 minutes, until the sweet potato is slightly softened. Add the sweet red pepper, cook for 5-10 more minutes, then stir in the spinach and cook until wilted.
Stir in the fish sauce. Remove from the heat and add the lime juice.
I like to serve a whole grain alternative with my sweet potato red Thai curry -- usually whole grain brown basmati rice or barley. Even quinoa or buckwheat make great options.