It is important that the oil temperature is close to 190 degrees F. If it's too cool, the scallions won’t release their sweetness and have a harsh, raw aftertaste. If it's too hot, the flavor and color of the scallions will lose vibrancy. If done correctly, the scallion oil will retain its verdant color for up to 5 days. The tofu here is fried, but you could poach it instead, or pick up a package of fried tofu available at many Asian markets and reheat.