Prepare all vegetables by washing and slicing the onion, bell peppers, broccoli, and carrots. Mince the garlic.
In a small bowl, mix the soy sauce, oyster sauce, hoisin sauce, sesame oil, and black pepper. Dissolve the cornstarch in water and set aside.
Heat olive oil in a skillet or wok over medium-high heat. Add ground beef and cook until browned, about five to seven minutes. Remove beef and set aside.
In the same skillet, sauté garlic and onions for one to two minutes. Add bell peppers, broccoli, and carrots, stir-frying for four to five minutes until crisp-tender.
Return the cooked beef to the skillet with vegetables. Pour in the sauce and stir to coat. Add the cornstarch mixture and stir until the sauce thickens, one to two minutes.
Serve over steamed rice and optionally garnish with green onions or sesame seeds.