Ground Beef and Broccoli Stir Fry

Name: Ground Beef and Broccoli Stir Fry
Ingredients: 1 cup water; 6 tablespoons lower-sodium soy sauce; 3 tablespoons packed light brown sugar; 1 tablespoon cornstarch; 3 cloves garlic , minced; 1 tablespoon minced fresh ginger (from 1-inch piece); 2 teaspoons unseasoned rice vinegar; 3 tablespoons neutral oil (such as canola), divided; 12 ounces (about 5 1/4 cups) fresh broccoli florets; 1 pound 90/10 lean ground beef; 1/2 teaspoon kosher salt; 2 teaspoons toasted sesame seeds (optional); 2 green onions , thinly sliced (optional); Steamed white rice , for serving