01 - In a small bowl, whisk together the soy sauce, oyster sauce, mirin, sesame oil, and sugar until the sugar dissolves. Set aside.
02 - Prepare the udon noodles according to the package instructions. Drain thoroughly and set aside.
03 - Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the shrimp and stir-fry for 2 to 3 minutes until pink and opaque. Remove the shrimp and set aside.
04 - Add the remaining tablespoon of vegetable oil to the pan. Sauté the garlic and ginger for about 30 seconds until fragrant.
05 - Add the onion, carrot, and bell pepper to the pan. Stir-fry for 3 to 4 minutes until just tender-crisp.
06 - Return the cooked shrimp to the pan and add the drained udon noodles. Pour the prepared sauce over everything, tossing with tongs or a spatula to coat evenly.
07 - Add the spinach or bok choy and sliced green onions. Stir-fry for 1 to 2 minutes until the greens are just wilted.
08 - Transfer to serving plates and garnish with toasted sesame seeds, shredded nori, and lime wedges as desired. Serve immediately.