Slice the flank steak thinly against the grain into strips about ¼ inch thick.

In a medium bowl, mix together soy sauce, brown sugar, minced garlic, grated ginger, and water until well combined.

Place the sliced flank steak in the slow cooker and pour the sauce mixture over it, ensuring each piece is coated.

Cover and cook on low for 3-4 hours or on high for 1.5-2 hours, until beef is tender.

For thicker sauce, mix cornstarch with water and stir into the slow cooker 30 minutes before serving.

Serve over rice, noodles, or in lettuce wraps.