Into a bowl, add Sirloin Steak (1 pound) and Dark Soy Sauce (2 tablespoon), and mix to coat. Let marinate for 15 minutes.
In a pot, warm Sesame Oil (3 tablespoon). Add Onion (1) and Green Bell Pepper (1). Cook over medium heat until onion is translucent, about 2-3 minutes.
Add beef and stir to combine. Cook over medium-high heat until beef is browned, about 2-3 minutes.
Add Brown Sugar (1/3 cup), Salt (1/2 teaspoon), and Ground Black Pepper (1/2 teaspoon). Mix.
Add Oyster Sauce (1/3 cup) and Water (to taste) to just cover the beef. Bring to a boil, then reduce to a simmer. Cover and cook for 20 minutes, stirring once halfway through.
In a small bowl, combine cold Water (4 tablespoon) and Corn Starch (4 tablespoon). Add it to the pot with the beef. If the sauce is too thick, add additional water. Cover and let the mixture simmer for another 5 minutes.
Serve over White Rice (to taste). Enjoy!