I'm not 100% where this goes, but lets get some lists together for penance for missed workouts or diet cheats.

Something like 1 3scoop bowl of icecream = 2 extra 30min HIIT sessions per week.

Any ideas? Is this a bad idea? Thoughts?

I'm not really sure where you're going with that, but trying to justify a cheat with extra exercise is not the way to go IMO.

It's easier to work smarter than harder. In other words, have 1 bowl of ice cream for a cheat and eat clean for all other meals.

My vote is for Bad Idea.

A. You create negative connotations for exercise.
Do you want to think of exercise as a Penance or as a Fun hobby?
Which of these options do you think will be sustainable for the long
term? (I.E Years and years to come).

B. 2-3 small cheats and your all out of time to fit all your training
sessions a week. (assuming you are human and can't do 3 30mins
HIIT session a day)

C. You are not "paying" the penance immediately. You could easily
go into "overdraft" mode.

If you really want some penance I'll be happy to provide my bank account details for you to transfer 50$ per none planned cheat meal. But planning some small cheats into your weekly plan or setting aside ~200 calories for treats daily (as part of your planned intake) might just be a wiser choice.

Shahar.