Creating Japchae can be straightforward if you follow these simple steps:

1. Soak Noodles: Place sweet potato glass noodles in a bowl of warm water for about 30 minutes or until softened. Drain and set aside.
2. Prepare Vegetables: While the noodles are soaking, prepare your vegetables. Slice the onion, carrot, bell pepper, and mushrooms.
3. Cook Beef: Heat 1 tablespoon of vegetable oil in a large skillet over medium-high heat. Add the sliced beef and cook until browned, about 3-4 minutes. Season with salt and pepper. Remove from the skillet and set aside.
4. Sauté Vegetables: In the same skillet, add the onion, carrot, and mushrooms. Sauté for about 5 minutes until softened. Add the bell pepper and spinach, cooking for an additional 2-3 minutes until the spinach wilts.
5. Combine Noodles and Beef: Add the drained noodles to the skillet along with the cooked beef. Stir to combine.
6. Season: In a small bowl, mix together the soy sauce, sesame oil, sugar, and minced garlic. Pour this mixture over the noodles and stir-fry everything together for about 3-4 minutes, ensuring that the noodles are well-coated.
7. Serve: Transfer to a serving platter and sprinkle sesame seeds on top as garnish. Enjoy your Japchae warm or at room temperature.