Heat a pot over medium heat. Add the amaranth to the pot and toast until fragrant/golden; 1 to 2 minutes. Add water, coconut milk, and salt to the pot. Bring the mixture to a boil, and reduce to a simmer, cover and let simmer for 20 minutes. Remove from heat and let sit for 5 to 10 more minutes to thicken amaranth.

In a separate pot, combine the ingredients for the rhubarb topping. Heat over medium low until rhubarb is cooked and has broken down. Taste and add extra sweetener or cinnamon as desired.

Divide the amaranth into two bowls and stir in the rhubarb mixture. Sprinkle with toasted coconut and a drizzle of coconut milk, if desired.