Preheat oven to 200 degrees F. Heat oil in a large skillet set over medium-high heat. Carefully, and lightly, coat the tofu in the cornstarch. Reserve the leftover cornstarch. Lightly brown the tofu on both sides, remove from the pan, dab on paper towels to remove excess oil, and then keep warm in the oven.
Drain all but 2 Tbsp. of oil from the pan. When pan is hot again add the vegetables and chili flakes and stir-fry 3–4 minutes. Mix 1 Tbsp. of the left over cornstarch into the teriyaki sauce/water mixture. Pour into the pan and cook, stirring, until a sauce forms around the vegetables. Arrange tofu on the outer edges of two plates. Top with stir-fried vegetables and serve.