The frozen meat and chicken imported from non-Islamic countries have the following sentence, "Halal slaughtered ". Is it really Halal? Who monitors the slaugtering?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Allah has made the meat slaughtered by the People of Book Halal (permissible) for Muslims Allah Says (interpretation of meaning): {Made lawful to you this day are At­Tayyibât [all kinds of Halâl (lawful) foods, which Allâh has made lawful (meat of slaughtered eatable animals, etc., milk products, fats, vegetables and fruits, etc.). The food (slaughtered cattle, eatable animals, etc.) of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them. (Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians) before your time, when you have given their due Mahr (bridal money given by the husband to his wife at the time of marriage), desiring chastity (i.e. taking them in legal wedlock) not committing illegal sexual intercourse, nor taking them as girl-friends. And whosoever disbelieves in the Oneness of Allâh and in all the other Articles of Faith [i.e. His (Allâh's), Angels, His Holy Books, His Messengers, the Day of Resurrection and Al­Qadar (Divine Preordainments)], then fruitless is his work, and in the Hereafter he will be among the losers.} [5: 5].
If the People of Book perform slaughtering as the known way, that is cutting the jugular vein and the pharynx then it is permissible for Muslims. But if they kill animals by electric shock or strangling or the like, then it becomes maytah (animal not slaughtered according to the above mentioned way) and eating such meat is forbidden for a Muslim.
If the imported meat to the Muslim countries is from the Christian and Jewish countries, it is Halal for Muslims. But if it proven that the meat is not slaughtered according to Sharia then a Muslim should not eat it. As long as Allah made it permissible for us we should not avoid eating it unless we know undoubtedly that eating it is Haram.
Eating the meat imported from a secular country or a polytheist country or a communist country is forbidden regardless of what is written on it, unless you know that such meat is slaughtered according to Sharia by a Muslim or a person of the Book. The same rule applies if the meat imported is from countries of people of the Book but who do not slaught according to Sharia or where the persons who slaughter are neither Muslims nor from the people of the Book.
If we do not know how the meat imported from the countries of people of the Book is slaughtered, then it is assumed to be Halal.
Allah knows best.