In a saucepan over medium-low heat, heat 4 teaspoons of vegetable oil until hot but not smoking. Add minced ginger and chopped garlic, stirring for about 30 seconds until fragrant.

Pour in soy sauce and water, then stir. Add brown sugar and mix well before bringing to a gentle boil for 2-3 minutes.

Remove from heat once the sauce thickens slightly and set aside.

Slice the flank steak against the grain into ¼ inch thick pieces at a 45-degree angle.

Toss the steak pieces in a large bowl with ½ cup cornstarch, ensuring each piece is generously coated. Let rest for 20 minutes.

Sprinkle the coated beef with ½ teaspoon salt and toss for an even coat.

In a large wok or skillet, heat 1 cup of oil over medium heat until hot but not smoking. Add the beef, ensuring not to overcrowd.

Stir frequently for about 2-3 minutes until browned. Remove with a slotted spoon to a paper towel-lined plate to catch excess oil. Carefully pour remaining oil out.

Return the beef to the empty pan, stir over medium-low heat for one minute. Add dried chilies if desired.

Pour in the prepared sauce and cook for one minute, stirring constantly. Add green onions and cook for an additional minute until beef is cooked through and onions are wilted.

Serve immediately over warm rice.