Prep the Noodles: Soak the sweet potato glass noodles in hot water for about 30 minutes, then drain and set aside.

Cook the Beef: Heat a tablespoon of vegetable oil over high heat, stir-fry the thinly sliced beef for 3-5 minutes until browned, then set aside.

Stir-Fry the Vegetables: In the same pan, add oil, then cook the carrots, bell peppers, and onions for 4-5 minutes. Add spinach until wilted, then return the beef to the pan.

Combine Everything: Add softened noodles to the skillet and toss with vegetables and beef.

Season the Dish: Pour soy sauce and sesame oil, toss to coat, and cook for an additional 2-3 minutes.

Finish and Serve: Serve the Japchae on a plate, garnished with green onions.