Oat is processed in different ways, as Synonym says pin head oats are steel cut.
Those types that are less processed and include all the fibre will normally have lower glycemic indices.
About different types of oats here
http://www.bbc.co.uk/dna/h2g2/A4888858
Incidently the lowest gi and gl porridge I found on the giindex database was Sainsburys jumbo rolled oats made with semi-skimmed milk which had a gi of 40. and gl of 9 (not many UK brands have been 'officially' tested, but unsurprisingly those made traditionally with water have a higher gi) The highest was an unnamed brand of instant oat cereal made with water with a gi of 83.