I was watching this short clip https://www.youtube.com/watch?v=6RY-c65As_c and in particular Sh Hamza Yusuf says Muslims are eating meat far too much. What is the evidence from the Book and Sunnah?
It's a matter of achieving a balance that works for you; there's a wide range that's halal. There's a unspecific restriction in the Qur'an:
O children of Adam, take your adornment at every masjid, and eat and drink, but be not excessive. Indeed, He likes not those who commit excess.
And the Prophet gave his advice on how much to eat in general:
A human being fills no worse vessel than his stomach. It is sufficient for a human being to eat a few mouthfuls to keep his spine straight. But if he must (fill it), then one third of food, one third for drink and one third for air.
Sunan Ibn Majah [grade: sahih]
The above apply not only to meat. There are verses of the Qur'an which encourage eating (lawful) meat:
So eat of that [meat] upon which the name of Allah has been mentioned, if you are believers in His verses. And why should you not eat of that upon which the name of Allah has been mentioned while He has explained in detail to you what He has forbidden you, excepting that to which you are compelled. ...
Unsurprisingly, there's ahadith describing the Prophet eating meat (e.g. Sahih al-Bukhari 5404).
Regarding being a vegetarian:
The closest I've seen to a direct restriction on eating meat are some ahadith (but I'm unsure about their authenticity):
Hazrat Ali Ibn Abi Talib, the cousin and son-in-law of Prophet Muhammad, the fourth Khalifa as per Sunni belief, has been quoted in Sharh Nahjul Balagha, as saying: “Do not make your stomach a graveyard of animals”.
I asked about the authenticity of this hadith here: What is the authenticity of the hadith "do not make your stomach a graveyard of animals"?
“At one time the Rasul of Allah said to his cousin ‘Ali, ‘O ‘Ali, you should not eat meat. If you eat meat for 40 days, those qualities will come within you. Because of that, your human qualities will change, your compassionate qualities will change, and the essence of your body will change.’ “
I asked about this latter one here: What is the authenticity of the hadith "if you eat meat for 40 days, those qualities will come within you"? It appears to be considered more reliable in Shia Islam.
These are popular ahadith on Muslim vegetarian websites.
The majority types of meats are permissible (Halal) and can be eaten to any wanted quantity. However there are some types of foods that are prohibited, for more information click here.