I was talking to a DAFNE dietician about this the other day, and she admitted that although they are supposed to teach that pulses don't need to be covered by insulin, experience had taught her that everyone is slightly different. So now she says, err on the side of caution but you may need to inject for it; it's a question of working out what works for you.
which is all basically what noblehead said, but I thought it was interesting that very specialist HCPs have begun to realise this/teach this too. An ordinary dietician without experience might not have reached this level of understanding though.
The other thing to bear in mind is that if you are eating fat with the lentils, (eg ghee) it will make the GI of the whole meal a bit lower.