Prepare noodles according to package directions. Drain well.
While noodles soak, heat canola oil in a large nonstick skillet over medium-high heat. Add radish and cucumber; saute 1 minute, or until tender. Stir in 1/2 teaspoon salt, the next 3 ingredients, and the noodles. Sauté 1 minute.
Combine noodle mixture and watercress. Wipe skillet clean with paper towels. Sprinkle tofu with the remaining 1/4 teaspoon salt. Heat the sesame oil in the skillet over medium-high heat. Add tofu, and sauté 2 minutes. Serve the tofu over the noodle mixture. Sprinkle with sesame seeds.