Set on a large plate or baking sheet, seam-side down, and freeze for at least 2 hours. I let them sit for 4 hours because they need to be frozen solid.
Combine sugar and cinnamon in a shallow plate and set aside.
Heat the oil in a deep pan over medium-high heat.
Fry the chimichangas for about 1 minute, flip and continue to cook for a few seconds longer.