Preheat oven to 425°F.
Place whole sweet potatoes on a baking sheet lined with parchment paper and bake for 45 minutes to 1 hour, or until very soft (depends on size of potatoes).
While potatoes are baking, combine bottom layer ingredients in a medium pot. Bring to a boil, then reduce heat and simmer, covered, for 15 minutes. Remove from heat.
Combine middle layer ingredients in a medium pot. Bring to a boil, then reduce heat and simmer, uncovered, for 15 minutes. Remove from heat.
Grease a 9“ x 13” glass baking dish with a bit of coconut oil. Pour in the bottom layer (buckwheat), using a spatula to spread evenly in the dish. Let this sit for at least 5 minutes, then add the middle layer (beans) and spread out evenly with a spatula.
When sweet potatoes are soft, remove from oven and let sit until cool enough to handle. Reduce oven temperature to 375°F. Scoop out inside of sweet potatoes into large bowl and combine with remaining top layer ingredients. Mash well with a fork or potato masher.
Add the top layer (mashed sweet potato) to baking dish and spread out evenly and gently with spatula.
Place dish in oven. Bake for 15 minutes and serve.
Notes:
If not serving right away, save the final step until right before serving, but allow 30 minutes to fully reheat.