Preheat oven to 400°. Blot tofu dry. Cut into 3/4-in. cubes. Place on a clean kitchen towel; cover with another towel. Place a cutting board on top; gently place a large cast iron skillet on top. Let stand 10 minutes. , Meanwhile, in a shallow dish, whisk together soy sauce, olive oil, sesame oil, salt, garlic powder and pepper. Place cornstarch in a separate shallow dish. Add tofu to soy mixture; turn to coat. Add tofu, a few pieces at a time, to the cornstarch; toss to coat. Place on a parchment-lined baking sheet. Bake until cubes are golden brown and crispy, 25-30 minutes, turning halfway through. Garnish with green onions, if desired.