Begin by boiling water in a pot. Once boiling, add the yakisoba noodles and cook according to the package instructions (usually 3-5 minutes). Drain and set aside.
In a large skillet or wok, heat the vegetable oil over medium-high heat.
Add the minced garlic and ginger to the oil and sauté for about 30 seconds until fragrant.
Add the shrimp to the skillet and cook for about 3-4 minutes until the shrimp turn pink and opaque. Remove the shrimp and set aside.
In the same skillet, add the sliced cabbage, carrots, and bell peppers. Stir-fry the vegetables for about 4-5 minutes until they are tender but still crisp.
Return the cooked shrimp to the skillet. Add the cooked yakisoba noodles.
Pour in the soy sauce, oyster sauce, and mirin (if using). Toss everything together until well combined and heated through, about 2-3 minutes.
Taste and adjust seasoning with salt and pepper if needed.
Serve hot, garnished with chopped green onions and sesame seeds if desired.