Heat the sesame seed and vegetable oils in a wok or large skillet over medium-high heat and saute the garlic for about 30 seconds
Add the ground beef and cook until no pink is left in it. Drain any excess fat.
Throw in the shredded cabbage, red bell pepper, and half of the green onions. Cook until the veggies start to soften, about 5-7 mins
Pour in the soy sauce, rice vinegar, and add the black pepper and red pepper flakes. Cook for another two minutes
Make a slurry by dissolving the cornstarch in ½ cup of water. Pour it into the wok and cook until the sauce thickens, about 3-4 minutes more. Season with salt if needed. Serve with the remanining green onions on top