Veggie Udon Stir Fry

Name: Veggie Udon Stir-Fry
Ingredients: 1/4 cup soy sauce; 2 Tbsp. vegetarian oyster sauce or oyster sauce; 1 Tbsp. mirin; 2 cloves garlic, grated on a Microplane zester (1 tsp.); 1 Tbsp. toasted sesame oil; 2 bell peppers, sliced (about 2 cups); 1 large carrot, peeled and thinly sliced on the bias (about 1 1⁄4 cups); 1 small white onion, thinly sliced (about 1 cup); 3 8.81-oz. blocks frozen precooked udon stir-fry noodles; 4 cups shredded napa cabbage (from 1 head cabbage); Sliced scallions, for garnish