Should I pray Asr, Dhuhr, or both if I intended Dhuhr with an Imam who was later found to be praying Asr, knowing that I caught two Rak'ahs with him, and that the times for the two prayers are close in Tunisia, and that we follow the Maliki school of thought, and is the order of prayers obligatory?

The Maliki school of thought holds that it is not valid for someone performing a fard (obligatory) prayer to follow an imam who is performing a different fard prayer. Therefore, according to the Maliki view, the Dhuhr prayer you performed behind someone praying Asr is not considered sufficient for you, and you must repeat it. According to the Malikis, you are obligated to pray Dhuhr first, then Asr, observing the correct sequence between them. As for the Shafi'i school and a group of verified scholars: the unity of intention between the imam and the follower is not a condition. Thus, it is valid for someone performing a fard prayer to follow someone performing a supererogatory (nafl) prayer, or someone performing a different fard prayer. This latter opinion is the one considered authoritative for issuing fatwas.