Chinese Pepper Steak with Onions

• 2 lbs Ribeye steak (2-inch long thin slices)
• 1 red bell pepper (chopped into bite-size pieces)
• 1 green bell pepper (chopped into bite-size pieces)
• 1 medium white onion (chopped into bite-size pieces)
• 2 tbsp vegetable oil (divided in half)

Sauce

• 3 cloves garlic (minced)
• 1 tsp black pepper
• ½ tsp ginger (minced)
• 2 tbsp brown sugar
• ⅓ cup soy sauce
• 1¼ cups beef broth
• 2 tbsp rice vinegar
• 1 tsp sesame oil
• 2 tbsp cornstarch