In a pan add oil, and once hot, add onions, garlic and ginger. Stir fry till fragrant.

Add the beef slices next, and allow to cook.

Add the dark soy sauce, oyster sauce, tomato paste and black pepper and combine with the beef. Add water to form a liquid sauce. You can combine these ingredients in a bowl beforehand for efficiency.

Add the udon to the sauce. Gently separate the noodles in the sauce until it's not a block. Allow the sauce to come to a boil.

Once it boils, add leafy vegetables.

Add the cornstarch slurry bit by bit, until sauce thickens. Serve!