French Onion Meatball Subs

Ingredients

• 1 pound Ground Beef (93% lean or leaner)
• 1 egg, beaten
• 1 packet (1 ounce) onion soup mix
• 1/4 cup dry bread crumbs
• 1/4 teaspoon ground black pepper
• 2 tablespoons canola oil
• 1 packet (0.87 ounces) brown gravy mix
• 2 cups water
• 4 sub rolls, split
• 8 slices Gruyere cheese
• 1 green onion, thinly sliced
• 1-1/2 cups thinly sliced onion
• 2 tablespoons butter