To prepare the beef: In a large bowl, mix together 1 tablespoon of the canola oil, cornstarch, salt, pepper, and oyster sauce. Toss in the cubes of steak to coat. Cover and set aside for 30 minutes.
To make the red wine sauce: In a medium bowl, whisk together the red wine, Maggi sauce, Worcestershire sauce, and sugar. Cover and set aside.
In a large skillet or wok, drizzle the remaining 1 tablespoon canola oil for high heat. Once heated, reduce heat to medium. Add half of the steak and cook on one side for 3 minutes. Flip and cook the other side for a minute. Add 2 teaspoons of the garlic and shake the pan for 30 seconds. Pour in 2 tablespoons of the prepared red wine sauce and continue to shake the pan for 2 minutes for browned, medium rare steak. Transfer to serving pan and clean out the pan. Repeat these steps for the remaining half of the marinated steak. Once the second batch is done, transfer to serving plate and return pan to medium heat. Add the sliced onions and cook until softened, 1-2 minutes. Serve over the meat with the tomato wedges and lettuce/roasted potatoes.