Add 1 tablespoon oil to a large nonstick skillet or wok set over medium-high heat. Once the oil is hot, add the beef in batches and cook, stirring occasionally, until it is browned on all sides, about 2 minutes. (Do not overcook it, as it will continue cooking alongside the vegetables and sauce.) Using a slotted spoon, transfer the beef to a plate and leave all drippings in the pan.
Add the remaining 1 tablespoon oil to the pan then add the bell peppers, snap peas and carrots and cook, stirring constantly, for 2 minutes. (The vegetables should remain crisp-tender.)
Stir in the sauce then bring it to a boil and cook, stirring occasionally, until the sauce is thick and syrupy, about 2 minutes. Return the beef and any juices to the pan and stir to combine.
Serve the stir-fry over rice or noodles.