Slow Cooker Mongolian Beef

1 pound flank steak, cut into bite-sized pieces
1/4 cup cornstarch
2 tsp. olive oil
1 onion, thinly sliced
1 Tbsp. minced garlic
3 large green onions, sliced diagonally into 1/2 inch pieces
1/2 cup soy sauce
1/2 cup water
1/2 cup brown sugar
1/2 tsp. minced fresh ginger root
1/2 cup hoisin sauce

1. Place flank steak and cornstarch into a resealable plastic bag. Shake the bag to evenly coat the flank steak with the cornstarch. Allow steak to rest for 10 minutes.
2. Heat olive oil in a large skillet over medium-heat. Cook and stir steak until evenly browned, 2 to 4 minutes. Place onion, garlic, flank steak, green onions, soy sauce, water, brown sugar, ginger, and hoisin sauce in a slow cooker. Cook on Low setting for about 4 hours.

Source: allrecipes.com