Cut the beef thinly against the grain. Slices should be about 1/4 inch thick. Trim any large pieces of fat. Dab the beef dry with paper towels and set aside.
In a large bowl or shallow pie plate, whisk together the flour, garlic powder, onion powder and fine sea salt.
Dredge the beef slices in flour mixture, shaking off excess flour. Set aside.
Heat the oil in a large skillet over medium heat. Working in batches so the meat doesn't touch, cook for 4-5 minutes or until the strips are fully cooked and browned on all sides. Remove to a plate and continue with the remaining beef.
In the same skillet, add the onion, garlic and ginger. If the skillet is dry, add a small amount of additional oil (1-2 teaspoons). Saute for 1-2 minutes.
Add the water, soy sauce and brown sugar, stirring until combined and sugar has dissolved. Bring to a low simmer.
Add the cooked beef back to the sauce, tossing to coat and reducing to low heat. Sauce will thicken in 2-4 minutes. Stir in the chopped scallions.
Serve over rice or a bed of lettuce.
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