Prepare zucchini “noodles”: Trim the ends of the zucchini. With a vegetable peeler, shave the zucchini lengthwise into long, thin strips. When you get to the seedy center of the zucchini, turn it over and slice from the other side until you get to the center again. Discard the center. Stack a few strips at a time and slice into 1/4-inch thick “spaghetti.” (Note: If you have a mandoline slicer, use the julienne blade to slice the zucchini into long, thin strips, discarding the strips from the seedy center.)

Place a large colander over a large bowl. Add the zucchini and toss with the salt; let stand 15 minutes (this draws out some of the water and makes the zucchini crisper). Rinse well and pat dry.

Meanwhile, prepare the pasta according to package directions, omitting salt; drain and rinse in a colander and set aside. (You’ll have about 1 3/4 cups.)

Heat the oil in a large nonstick skillet or wok over medium-high heat. Add the scallions and ginger and cook, stirring, until the scallions are softened, about 3 minutes. Whisk together the broth, soy sauce, vinegar, and cornstarch in a small bowl. Add the broth mixture to the skillet; bring to a boil. Reduce the heat and simmer, stirring occasionally, until the sauce bubbles and thickens, 3 – 4 minutes.

Gently stir in the zucchini “spaghetti” and heat through. Sprinkle with the chopped bell pepper and red pepper flakes, if using; serve at once.