Slice tofu into 3-4 horizontal slices. Drain well by placing between 2 cookie sheets lined with paper towels. Weight down the top cookie sheet with canned goods or a cast iron skillet to "press" the moisture out of the tofu. Keep changing the paper towels until no more moisture can be pressed from the tofu. This is the key to crispy tofu. Once dry, cut the tofu up into 1" cubes and toss with 1 tablespoon of cornstarch to coat.
While drying the tofu, prepare the sauce. Combine sesame oil, ginger, garlic, rice vinegar, soy sauce, red pepper flakes, brown sugar, 1 tablespoon cornstarch and water. Mix in blender or food processor until completely smooth. Set aside.
In a large skillet over medium-high heat, add 1 tablespoons of oil and swirl to coat pan. Add the cubed tofu to the pan and fry for 3-5 minutes. Flip the tofu as needed to brown all sides. Add 2 tablespoons of the prepared sauce to the tofu and allow to cook for an additional 2-3 minutes. When the tofu is carmelized, remove to plate and keep warm.
Add the remaining 1 tablespoon of oil to the pan. Add the veggies and toss to coat. Cook the veggies for 3-4 minutes or just to al dente. Add the sauce and let it thicken just slightly. Add the tofu and sesame seeds and stir to coat. Cook for an additional 1-2 minutes or until the tofu has soaked up all the flavors.
Serve warm with rice or quinoa or on its own. Eat right away as the tofu will lose its crispiness as it sits and cools.