Whisk together ponzu, soy sauce, oyster sauce and cornstarch and set aside.
Pat steak dry and season with salt and pepper.
Heat wok or large skillet over very high heat.
When hot, add half of the steak so the meat gets a good sear and cook, tossing occasionally until browned on all sides, about 2 minutes total.
Transfer to a plate, repeat with the remaining meat; set aside.
Reduce the heat to medium-high, add the oil, scallion whites, garlic, ginger, carrots, water chestnuts, and red pepper to the wok and toss frequently until beginning to soften, about 2 minutes.
Add baby bok choy and zucchini and cook for an additional 2 minutes until the leaves turn bright green.
Return the steak back to wok and pour the sauce mixture.
Bring to a boil and allow to cook through and reduce, about 1 to 2 minutes more.
Garnish with scallion greens and serve.