In a small bowl combine soy sauce, sugar, rice vinegar, sesame oil, and pepper. Stir and set aside. 

Place noodles into a pot of boiling water and cook just until broken up (don’t cook all the way). Drain and rinse with cold water. Set aside. 

Heat a large frying pan over medium-high heat. Add 2-3 tablespoons of cooking oil, and allow to heat until it starts to smoke a little. Add in the spinach, carrots, bell pepper, mushrooms, and garlic. Sauté vegetables for 2-3 minutes until slightly tender, stirring constantly. Add snow peas and green onions and sauté for 1 more minute.

Add the noodles and the teriyaki sauce. Cook on high heat for 1-2 minutes, stirring constantly (tongs will work best for this). If you notice it sticking to the bottom, add in a little more oil and lower the heat slightly. The sauce should be thickened slightly and coating the noodles nicely. Serve immediately.