Whisk oyster sauce, soy sauce, brown sugar, and chili flakes in a small bowl to create the glaze.
Lay beef strips flat and place a portion of bell pepper, carrot, scallion, and 2-3 basil leaves at one end of each strip.
Roll the beef tightly around the vegetables and secure each roll with a wooden toothpick.
Heat vegetable oil in a large skillet or wok over medium-high heat.
Place beef rolls in the skillet seam-side down and sear for 2 to 3 minutes per side until well-browned and beef is cooked through.
Add minced garlic to the skillet and cook for 30 seconds until fragrant.
Pour the prepared sauce mixture over the rolls and toss gently for 1 minute until the glaze thickens and coats the beef.
Remove toothpicks carefully before serving hot.