Prepare the Stir-Fry Sauce
In a medium bowl, whisk together the water, soy sauce, brown sugar, and cornstarch until the cornstarch and sugar are fully dissolved. Stir in the minced garlic, ginger, and rice vinegar. Set the sauce aside.

Cook the Broccoli
Heat 2 tablespoons of oil in a large skillet or wok over medium-high heat. Add the broccoli florets and a pinch of salt. Cook, stirring occasionally, for 4 to 5 minutes until the broccoli is bright green and barely tender. Transfer the cooked broccoli to a plate.

Brown the Ground Beef
Return the skillet to medium-high heat and add the remaining tablespoon of oil. Add the ground beef and 1/2 teaspoon of kosher salt. Cook for 5 to 7 minutes, breaking the meat into crumbles, until it’s browned. Drain any excess fat.

Combine and Thicken
Give the prepared sauce a quick stir and pour it into the skillet with the browned beef. Cook, stirring constantly, for about 2 minutes, or until the sauce begins to bubble and thicken. Add the cooked broccoli back into the skillet and stir until it’s heated through and coated in the sauce.

Garnish and Serve
Serve the dish hot over steamed white rice. Garnish with toasted sesame seeds and thinly sliced green onions if desired.