In a medium pot, bring water to a boil. Add piloncillo bars, stir until dissolved. Add cinnamon stick. Reduce heat to low. With a spice grinder, grind the lentils to a powder. Slowly add the ground lentils to the pot, stir constantly. Add the plant milk slowly. Bring to a boil, then reduce heat to low. Stir in the rice flour. Continue to simmer and stir for about 10 minutes, until the mixture thickens.
Ladle into mugs and serve hot.
Note: Piloncillo is a minimally-processed Mexican sugar made from sugar cane juice. It has a unique flavor similar to molasses, with smokey, earthy elements. It comes in cones or bars and can be found in Latin grocers or online.