1. Cut tofu lengthwise into 2 (1-inch-thick) slices. Cut each slice lengthwise into 4 (1-inch-thick) strips. Place tofu on several layers of heavy-duty paper towels. Cover tofu with additional paper towels; top with a cast-iron skillet or other heavy pan. Let stand 15 minutes.
2. Heat a large skillet over medium-high heat. Sprinkle tofu with salt and pepper. Add canola oil to pan, and swirl to coat. Add tofu to pan; cook 10 minutes or until browned, turning to brown all sides. Remove tofu from pan, and drain on paper towels. Add cashews to pan; cook 30 seconds or until nuts are just beginning to brown. Remove nuts with a slotted spoon, and coarsely chop. Cut tofu strips crosswise into 1-inch cubes. Combine 1/4 cup vinegar, 3 tablespoons water, and sugar in a small saucepan; bring to a boil. Remove from heat; add carrots and radish. Let stand 15 minutes; drain. Combine mayonnaise, Sriracha, and 1 teaspoon vinegar in a small bowl, stirring with a whisk.
3. Working with 1 tortilla at a time, heat tortillas over medium-high heat directly on the eye of a burner for about 15 seconds on each side or until lightly charred. Arrange about 1/4 cup carrot mixture in center of each tortilla; top with 4 tofu pieces, about 1/2 teaspoon cashews, about 1 teaspoon mayonnaise mixture, and 1 1/2 teaspoons green onions.