In a small bowl add 1/4 of the arrowroot powder to the water and whisk well. Set aside.
In a small saucepan over medium-low heat, add 1/4 of the oil. Once hot, add the garlic and ginger and cook until fragrant, about 1 to 2 minutes. Then add the sriracha, ketchup, rice vinegar, tamari and the arrowroot mixture. Whisk well to combine and let it come to a boil. Reduce the heat and let it simmer for about 5 minutes. Turn off the heat.
In a large bowl, toss the tofu with the remaining arrowroot powder and remaining oil. Toss gently to combine, ensuring the tofu is coated and no white powder remains.
Heat a cast-iron skillet over medium heat. Once hot, add the cubed tofu and cook until crispy on one side, about 5 minutes. Flip and cook for another 5 minutes, until crispy.
Turn the heat off, but leave the skillet on the same burner. Add the sweet and sour sauce to the tofu and toss to combine. Divide onto plates and top with cilantro and sesame seeds, if using. Enjoy!