Cook the sweet potato glass noodles according to package instructions, about 6-8 minutes until transparent and tender. Drain and rinse under cold water.

In a large skillet, heat 1-2 tablespoons of oil over medium-high heat. Stir-fry the thinly sliced beef for 3-4 minutes until browned.

In the same skillet, add more oil if needed and stir-fry the chopped carrots, bell peppers, and spinach for 3-5 minutes until tender.

Return the cooked beef to the skillet, add the noodles, soy sauce, and sesame oil. Toss for 2-3 minutes until well coated.

Cook for an additional 1-2 minutes and garnish with green onions before serving.