In a medium size pan, add the glutinous rice and water. Cook on medium-high heat until bubbling, and rice has absorbed most of the moisture. This should take around 5-7 minutes.
Add cocoa powder and sugar. Stir consistenly until they are fully mixed in. Add more water if the mixture gets too thick or the rice isn't cooked through.
Remove from heat and laddle the chocolate rice into small bowls. Serve with evaporated milk on top if desired.
Notes
For the traditional flavor, swap the cocoa powder for tablea (Filipino cacao tablets), and cook the rice in coconut or evaporated milk instead of all water.