Learn Turkish: On yedi avukat evli. - Seventeen lawyers are married.

It is very straightforward! You just take the word for ten (on) and add the single digit after it with a space. So on yedi is literally just "ten seven". There are no special irregular words for the teens.

Since there are seventeen lawyers, shouldn't it be avukatlar (plural)?

No, and this is a very important rule in Turkish: anytime you use a number before a noun to say how many there are, the noun must stay in its singular form. That is why it is on yedi avukat and never on yedi avukatlar.

I recognize ev (house) in the word evli. Is there a connection?

Exactly! The suffix -li means "with" or "having". So evli literally means "having a house" or "having a household", which is the Turkish way of saying "married".

Why isn't there a word for "are" in this sentence?

In Turkish, you don't always need a separate verb for "am", "is", or "are" in simple statements. Just putting the subject (on yedi avukat) and the descriptive word (evli) together is enough to mean "Seventeen lawyers are married."