Melt coconut oil in a small pot over medium heat. Cook and stir rhubarb, buckwheat, and a pinch of salt in hot oil for 1 minute. Add cinnamon; cook and stir until fragrant, about 30 seconds more.
Stir water into buckwheat mixture; bring to a boil. Reduce heat to low, cover the pot with a lid, and simmer until most of the water is absorbed and buckwheat is cooked, 15 to 20 minutes. Add flax, chia seeds, and honey; stir to combine.
I enjoy a little more of a tart flavor with this dish, but if you desire more of a sweet flavor, add a little more honey or maple. This makes 1 large serving. If you are eating it as a breakfast side dish, half the recipe.