Cook the udon noodles according to package instructions. Drain and set aside.
In a large skillet or wok, heat the vegetable oil over medium-high heat.
Add the shrimp to the skillet and cook for about 2-3 minutes until they turn pink and opaque. Remove the shrimp from the skillet and set aside.
In the same skillet, add the broccoli, bell peppers, and carrots. Stir-fry for about 5 minutes until the vegetables are tender-crisp.
Add the minced garlic and stir-fry for an additional 30 seconds until fragrant.
Return the cooked shrimp to the skillet and add the cooked udon noodles.
Pour in the soy sauce, oyster sauce, mirin, and sesame oil. Toss everything together until well combined and heated through, about 2-3 minutes.
Remove from heat and stir in the sliced green onions.
Serve hot, garnished with sesame seeds.