Assalamualaikum ustaz. In certain mosques, right after the Zohor sermon, the iqamah is immediately called out for the performance of prayer. Should I move to the back to perform sunnah qabliyah Zohor or continue to listen to the sermon until it’s over?
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions and all those who follow his footsteps until the Last Day.
First, as we all know it is sunnah for a person to perform the sunnah qabliah (before) and ba’diah (after) Zohor prayers. The most prioritized is four rakaat qabliah and four rakaat ba’diah, while the minimum is two rakaat each for qabliah and ba’diah. This is in accordance with a hadith from Aisyah R.Anha who said:
أَنَّ النَّبِىَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ كَانَ لاَ يَدَعُ أَرْبَعًا قَبْلَ الظُّهْرِ وَرَكْعَتَيْنِ قَبْلَ الْغَدَاةِ
The Prophet (ﷺ) never left four Rak’at before the Zuhr prayer, and two Rak’at before the Fajr prayer.” 
The next hadith:
كَانَ يُصَلِّى فِى بَيْتِى قَبْلَ الظُّهْرِ أَرْبَعًا ثُمَّ يَخْرُجُ فَيُصَلِّى بِالنَّاسِ ثُمَّ يَدْخُلُ فَيُصَلِّى رَكْعَتَيْنِ
“Before the noon prayer, he would pray four rak’as in my house, then go out and lead the people in prayer, then come in and pray two rak’as,” 
He also prayed two more rakaat after that. This is recorded in a hadith from Ummu Habibah R.Anha, she said the Prophet PBUH states:
مَنْ صَلَّى أَرْبَعِ رَكَعَاتٍ قَبْلَ الظُّهْرِ وَأَرْبَعًا بَعْدَهَا حَرَّمَهُ اللهُ عَلَى النَّارِ
“If anyone keeps on praying four rak’as before and four after the noon prayer, God will forbid that he be sent to hell.” 
Second, it is better for the mosque to not neglect the calling out of the adhan for the adhan is the eminence of Islam. It is also a means to inform the locals that the time for prayer has begun. Especially if it happens in a mosque which is the religious activities centre for the residents. From the fiqh angle, the adhan is sunnah muakkad for a prayer to be performed after it or the ones that have passed. 
This means that it isn’t an issue if, after the sermon, the adhan is called out. However, we suggest that it is best to pause the sermon for the Zohor’s adhan, then continue the rest of the sermon. Thus, both the rights of the preacher and prayer is harmoniously celebrated.
Third, there is no issue to perform the qabliah prayer and leave the sermon. It is better that after finishing the prayer and if the sermon is still ongoing to join the other congregants to listen to the sermon. Regarding praying at the back or the side prayer hall, in our opinion, this is prioritized if by doing so we can be mindful of our manners and avoid distracting the preacher if we pray in front of them. A hadith of the Prophet PBUH which became the basis of the Islamic legal maxim:
لَا ضَرَرَ وَلَا ضِرَارَ
“There is no injury nor return of injury.” 
We strengthen this with an argument of Rasullullah PBUH who commanded Sulaikun al-Ghatafani to perform the Tahiyyatul Masjid when the Prophet PBUH was delivering a sermon.
From Jabir bin Abdullah, he said:
جَاءَ سُلَيْكٌ الْغَطَفَانِىُّ يَوْمَ الْجُمُعَةِ وَرَسُولُ اللَّهِ -صلى الله عليه وسلم- يَخْطُبُ. فَجَلَسَ، فَقَالَ لَهُ: يَا سُلَيْكُ قُمْ فَارْكَعْ رَكْعَتَيْنِ وَتَجَوَّزْ فِيهِمَا – ثُمَّ قَالَ – إِذَا جَاءَ أَحَدُكُمْ يَوْمَ الْجُمُعَةِ وَالإِمَامُ يَخْطُبُ فَلْيَرْكَعْ رَكْعَتَيْنِ وَلْيَتَجَوَّزْ فِيهِمَا.
“Sulaik Ghatafani came on Friday when the Messenger of Allah (ﷺ) was delivering the sermon. He (Sulaik) sat down. He (the Holy Prophet) said to him: 0 Sulaik I stand and observe two rak’ahs and make them short, and then said: When any one of you comes on Friday, while the Imam delivers the sermon, he should observe two rak’ahs and should make them short.” 
According to Imam al-Nawawi, among the wisdoms of the above hadith is that if a person enters a mosque on a Friday and the imam is giving a sermon, it is sunnah to perform two rakaat of the tahiyyatul masjid and it is makruh to immediately sit before praying. It is sunnah to perform a simple and brief prayer so that he can listen to the sermon. 
We also advise the imam and congregants not to leave the sunnah qabliah prayer by straight away performing the Zohor prayer after the sermon to attain the rewards of the sunnah prayer. Abdullah bin Mughaffal RA narrated, the Prophet PBUH said:
بَيْنَ كُلِّ أَذَانَيْنِ صَلاَةٌ، بَيْنَ كُلِّ أَذَانَيْنِ صَلاَةٌ، ثُمَّ قَالَ فِي الثَّالِثَةِ: لِمَنْ شَاءَ
“Between every pair of adhans, there is a prayer; between every pair of adhans there is a prayer.” Then he said on repeating it a third time, “for him who wishes.”