The usual penalty if a Minister lies or misleads Parliament is for him or her to lose their Ministerial post. Since Mr Johnson is no longer a Minister that is not an option. The Speaker has no powers to investigate the truthfullness of any statements made in The House and although MPs may be held in contempt of Parliament, there is no sanctions available. The worst thing an MP can do is accuse another MP of lying. That will usually get him or her suspended for a few days.
In 2021 a petition to make lying to Parliament a criminal offence gained the necessary 100,000 signatures and was debated by MPs. The result was there were no plans to do so.
Working, as I do, on the assumption that all politicians tell lies, there is no reason to suspect that shortcoming does not suddenly disappear when they are in Parliament.