Prepare the udon noodles as per package instructions and set aside.
Heat sesame oil in a large pan or wok over medium-high heat.
Add minced garlic and stir-fry until fragrant, about 30 seconds.
Introduce the carrots and mushrooms, stir-frying for 2-3 minutes until softened.
Add bok choy and green onions, mixing well and cooking for another 2 minutes.
Add the cooked udon noodles, followed by soy sauce and mirin, stirring to combine.
If using, add your choice of protein and stir-fry until cooked through.
Serve immediately while hot, garnished with extra green onions if desired.