Step 1: In a preheated skillet, pour oil. Add garlic, then onion, stir constantly until onion is transparent. Add bell pepper. Add pork and cook until golden brown. Season with fish sauce. Stir for 3 minutes.
Step 2: Add water, bring to a boil. Add vegetables. Stir and cook for 5 minutes. Add oyster sauce. Cook for 3 minutes more. Serve hot.