Follow these simple steps to create your saucy, slurpable Japanese noodles:

1. Cook the Noodles: Bring a large pot of water to a boil. Cook the Japanese noodles according to the package instructions. Drain and set aside.
2. Prepare the Sauce: In a small bowl, mix soy sauce, mirin, sesame oil, and chili paste. Set aside.
3. Sauté Vegetables: In a large pan or wok, heat the vegetable oil over medium-high heat. Add minced garlic and grated ginger, stirring until fragrant (about 1 minute).
4. Add Vegetables: Toss in the julienned carrots, sliced bell pepper, and sliced mushrooms. Stir-fry for about 3-4 minutes until just tender.
5. Add Bok Choy: Incorporate the chopped bok choy and continue to stir-fry for an additional 2 minutes until wilted.
6. Combine Everything: Add the cooked noodles and desired protein to the pan. Pour the prepared sauce over the mixture. Toss everything together, ensuring the noodles are well-coated and heated through (about 2-3 minutes).
7. Garnish: Remove from heat and serve immediately, garnishing with sliced green onions and sesame seeds.

Make sure to taste and adjust seasoning if necessary before serving.