Slice the flank steak into thin strips across the grain. Place in a bowl and set aside while preparing the marinade/sauce.

Using a citrus zester, zest in the garlic cloves and fresh ginger. The onion didn't grate well using the zester, and it needs to be a wet paste, so I used my Cuisinart Smart Stick's chopper grinder attachment. Worked beautifully.

Stir in the pear juice, sweet soy sauce, sesame oil, brown sugar, and Gochugaru into the garlic, ginger and onion. Pour this marinade mixture over the sliced steak and massage in well to coat all the pieces. Cover and refrigerate at least 1 hour. I like to marinate for about 4-5 hours.

Mince the mushrooms. In a large skillet on high heat, add 1 tablespoon oil and fry the mushrooms, stirring, about 2-3 minutes. Remove from skillet and set aside.

Remove from heat and serve over rice. Enjoy!