In a blender, working in batches, blend the first 4 ingredients with 1 tbsp. salt and 2 tsp. pepper.
In a large pot, heat the oil over high. Add the onion; stir constantly, until soft, about 5 minutes. Stir in the rice, garlic and the cilantro mixture. Bring to a simmer over medium. Reduce the heat to low, cover and simmer until the rice is almost tender, 20 to 25 minutes. Remove from the heat; let stand, covered, 10 minutes.
Spread out between two large rimmed baking sheets. Cover loosely with paper towels and let cool completely.
Freeze in 2-cup portions.