Start by putting your flank steak in the freezer for about 20 minutes. This will firm up the meat enough so that you can slice it easier.

Remove from the freezer, trim off any excess fat. Slice the meat against the grain at an angle so that you have slices approximately 1/4 inch thick.

Dump your cornstarch into a large zip top bag and then add in your meat. Shake the bag so that all of the meat is covered in the cornstarch and then set aside for about 15 minutes so that the coating really sticks to the meat.

Next, make your sauce. Heat up your 2 tbl of oil over medium heat. Add in your ginger and garlic and right as they begin to cook through, add in your water and your soy sauce. Raise your heat to medium-high and add in your brown sugar.

Scoop out 1/4 cup of sauce and whisk in cornstarch to create a slurry. Pour slurry into sauce and stir to incorporate (repeat step with another tablespoon of cornstarch if you would like your sauce thicker)

Stir and let the sugar dissolve and then remove the sauce from the heat.

In a separate pot/wok/frying pan, heat up 2/3 cup vegetable oil over medium-high heat. When it is HOT, add in half of the meat and saute for 2 minutes or so and then with a slotted spoon remove the meat to a paper towel lined plate. Repeat with second half of the meat

Pour out the oil and wipe out the pot/wok/frying pan. Add the meat back into the pot and saute again for another minute so that the meat just starts to darken around the edges and then add in the sauce, cooking for another minute.

Remove the meat and serve immediately over rice or whatever you prefer and top with sliced green onions.