Cook the sweet potato noodles in boiling water for about 4 minutes. Drain and place into a bowl and set aside. Lightly drizzle a tablespoon or two of sesame oil over the noodles so they do not stick.
Using a large pan or wok, heat the vegetable oil over medium high heat. Add the onion slices and garlic and sauté for about 2 to 3 minutes. Add the bulgogi and cook until browned and cooked through.
Add the carrots and bell peppers and cook for about 5 to 6 minutes or, until the vegetables are beginning to soften. Add in the spinach and toss with the vegetables until slightly wilted and softened.
Turn the heat to low and add the cooked noodles, 2 tablespoons sesame oil, soy sauce, fish sauce and sugar. Toss to combine and cook for another 3 to 4 minutes.
Taste and adjust/add seasonings if needed. Garnish with green onions and sesame seeds. Serve and enjoy!