Chinese Pepper Steak with Onions & Peppers

Recipe
Ingredients:
1 ¼ lbs flank or sirloin steak, thinly sliced
1/2 red, 1/2 green, 1/2 yellow bell pepper, sliced
1 large onion, thick slices
2 garlic cloves, minced
1 tbsp ginger, optional
2-3 tbsp vegetable oil

Marinade:
2 tbsp soy sauce
1 tbsp oyster sauce
1 tbsp cornstarch
1 tsp sesame oil

Sauce Mix: