Preheat the oven to 350ºF, if you plan on baking the pancakes. If you'd like to grind your own buckwheat flour, simply pour raw buckwheat groats into a coffee grinder and grind until a fine flour-like texture is achieved, about 30 seconds. Measure the flour after grinding.
In a large bowl, mash the bananas (a few lumps are okay), then add in the ground buckwheat flour, oil, water, cinnamon, vanilla, baking soda, and vinegar. Stir well to create a fairly uniform batter. It will be slightly thicker than traditional pancake batter, not quite as runny.
To bake the pancakes, scoop the batter using a scant 1/4 cup measure, creating about 6 evenly sized mounds on a large lined baking sheet. Use the back of a spoon to spread the pancakes out, creating pancakes that are roughly 5- or 6-inches in diameter, and about 1/4-inch thick. Bake until the centers are firm, about 15 minutes at 350ºF.
If you prefer to pan-fry the pancakes, pour the scant 1/4-cup of batter into a greased skillet over medium heat, and use the back of a spoon to flatten the pancake into your desired size and thickness. (About 5 or 6 inches wide) Allow the top to bubble and the edges of the pancake to dry, about 4 or 5 minutes, then flip and cook through on the other side.
Serve warm, with fresh fruit and pure maple syrup, if desired.