1Combine broth, water, and 1/2 teaspoon of the salt in a small saucepan and bring to a boil over high heat. Add bulgur, stir to combine, and remove from heat. Cover and let sit until tender and all of the liquid has been absorbed, about 30 minutes.
2Meanwhile, place zucchini in a small bowl, sprinkle with remaining 1/2 teaspoon salt, and toss to combine; set aside.
3Heat oil in a large frying pan over medium-high heat. When it shimmers, add garlic and onion, season with freshly ground black pepper, and cook, stirring occasionally, until softened, about 5 minutes. Add zucchini and cook, stirring rarely, until well browned, about 5 minutes. Stir in vinegar and cook until smell has cooked off, about 30 seconds.
4Remove from heat and stir bulgur into zucchini mixture. Stir in fresh herbs, if using, and season to taste with salt and freshly ground black pepper.