When someone from outside the smoking group gets "in on the action" which is typically between two members of the original party that are already smoking and hit the bowl.
Person 1: You take so long to get ready.
Person 2: Let me cook.
Or maybe a more general way of using it would be things starting to come your way. The phrase ‘let me cook’ could be used as you’re telling everyone let me do my thing give me time and you’ll see.