Press the tofu to remove excess water, then cut into cubes. Toss the cubes with cornstarch until lightly coated.
Heat 2 tablespoons of the vegetable oil in a large skillet or wok over medium-high heat. Add the tofu and cook, turning occasionally, until golden and crispy on all sides, about 8 minutes. Remove and set aside.
Add the remaining oil to the skillet. Add the broccoli, bell pepper, and carrots, and stir-fry for 4-5 minutes until crisp-tender.
Add the garlic and ginger and cook for 30 seconds until fragrant. Whisk together the soy sauce, rice vinegar, maple syrup, and sesame oil, then pour into the skillet.
Return the tofu to the skillet and toss everything together until well coated and heated through.
Sprinkle with sesame seeds and green onions, and serve hot over rice.