Bring water, vegetable oil, and salt to a boil in a large pot. Add rice flour gradually, stirring constantly, until a smooth, thick dough forms, 2 to 3 minutes. Remove from heat and let cool.
Mix coconut, molasses, and cardamom together in a bowl to make filling.
Divide the cooled dough into 9 balls; flatten into thin discs. Place 1 tablespoon of the filling in the center of each disc. Wrap up dough around filling and roll into a ball between your palms.
Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add balls of dough, cover, and steam until a toothpick inserted into the center comes out clean, about 10 minutes.