In a bowl, combine the soy sauce, oyster sauce, fish sauce, brown sugar, minced garlic, and vegetable oil.
Add the thinly sliced beef and mix well to coat.
Cover and marinate in the refrigerator for at least 30 minutes.
In a small bowl, whisk together the lime juice, fish sauce, sugar, minced garlic, and sliced chilies (if using). Adjust seasoning to taste.
Heat 2 tablespoons of vegetable oil in a large skillet or wok over medium-high heat.
Add the marinated beef and stir-fry for 3-4 minutes, or until the beef is cooked through and slightly caramelized. Remove from the skillet and set aside.
In the same skillet, add a little more oil if needed.
Stir-fry the onion and bell pepper until softened, about 2-3 minutes.
Add the cherry tomatoes and cook for another 1-2 minutes until slightly softened.
Return the cooked beef to the skillet with the vegetables. Stir well to combine and heat through.
Enjoy your meal!