Cut tofu into large pieces (such as triangle shapes, about a dozen pieces).
In a small saucepan over medium heat, combine soy sauce, juice, vinegar, honey, ketchup, garlic, and pepper flakes. Stir, bring sauce to a simmer, and reduce heat. Add cornstarch (dissolved in 1 Tbsp water) and stir until sauce thickens, about one minute. Set aside.
Heat oil in a wok or skillet over high heat. Add tofu and pan-fry until all sides are golden brown. Transfer tofu to a plate and set aside.
In the same wok or skillet, over high heat, stir fry thicker white pieces of boy choy, bell pepper, and broccoli, adding 1-2 Tbsp of water to help vegetables cook easily. After 2 minutes, add leafy pieces of bok choy and green onion, stir frying for less than a minute. Add tofu and sauce. Stir to distribute sauce throughout evenly. Serve over white or brown rice.