Heat canola oil in a wok or heavy skillet over high heat. Add pork and stir-fry for 3 to 4 minutes, or until lightly browned. Add soy sauce; stir-fry one minute. Reduce heat to medium and add carrots. Cover and cook 3 minutes. Add green pepper, cashews and pepper flakes (if desired); stir-fry 3 to 4 minutes. Sprinkle with brown sugar and stir until dissolved, about 1 minute. Dissolve cornstarch in water. Add to wok or skillet. Stir and cook until sauce thickens and clears. Season with salt. Serve immediately with rice.