In a bowl, soak the vermicelli in hot water for 15 minutes. Drain the noodles, drop into a pot of boiling water for 30 seconds, and then rinse in cold water. Cut the noodles with kitchen shears.
Heat a large pan. Add 2 tablespoons sesame oil. Add the onion, carrot, red bell pepper, scallions, mushrooms, garlic, sugar, salt and pepper. Let cook for a few minutes, stirring, until the vegetables are cooked but still a little crisp. Transfer the vegetables to a bowl. To the pan add 1 more tablespoon sesame oil. Add the noodles, spinach, salt and pepper. Let cook for 1 to 2 minutes, stirring. Add to the vegetables with 1 tablespoon soy sauce and 1 tablespoon toasted sesame seeds and combine.
Transfer to a platter. Serve hot or at room temperature.