Mongolian Beef (Without Sauce)

Ingredients

• 1 1/2 lbs beef tenderloin, silverskin trimmed
• 1 tablespoon thin soy sauce
• 1 tablespoon dark soy sauce
• 1 1/2 tablespoons cornstarch
• 1 cucumber, peeled and sliced into 1/4-inch thick diagonal slices
• 2 1/2 tablespoons peanut oil
• 1 medium onion, cut in half and sliced thinly
• 1 1/2 inches cube gingerroot, peeled and thinly sliced
• 2 garlic cloves, peeled and thinly sliced