Dr. Lahiri is no catch out of central casting.
What does the highlighted part mean? I can't seem to find it in my dictionary.
Central Casting is not a source of "great" actors, or indeed of actors of any sort: it is a source of anonymous extras classified into established types. The performers within any particular classification are interchangeable; their function is not to create a character but to be recognizable on sight, without any lines. They’re essentially not people but props.
The sentence “Dr. Lahiri is no catch out of central casting” thus does not imply that the actor playing Dr. Lahiri is in any way inadequate to the part. Quite the contrary: it means that she does not conform to the stereotype of what constitutes a “catch”, and that she (and the writers) are free to develop her character in unexpected directions.
From the source: "She is defiantly idiosyncratic, a new type of character for TV".
He's no catch, in that of all the fish in the sea, Casting could have reeled in a better one.
It's simply an idiom, meaning not the best possible choice.
When used generically (as in the quote) central casting refers to a source of just the right person for some role or other. No catch is slang or idiom for “not highly desirable”. The quote as a whole indicates that Dr. Lahiri is not a wonderful and great-looking person.
Edit: Regarding catch, see sense 5 in wiktionary:
A find, in particular a boyfriend or girlfriend or prospective spouse. [eg]
Did you see his latest catch?
He's a good catch.
Applying that sense, no catch means “not good material for a boyfriend or girlfriend”, which I vaguely alluded to earlier via “not a wonderful and great-looking person”.
To understand the phrase, break it up into two parts" Dr. Lahari is no catch; out of central casting.
"Central casting" refers to a group of "random" actors/actresses, not a "star" player.
But even out of this (random) "central casting" group, Dr. Lahari is "no catch." That means "not a particularly good catch."
I accept (because I don't know otherwise) that central casting is merely a source of nondescript extras. But then the phrase "he is a catch out of central casting" would mean that the person concerned turned out to be much better than expected and therefore considered to be a 'proper' actor of some merit.
In a different context, one might hear the phrase "he is a real catch" in the context of people announcing that they are to be married. This means that the bride-to-be has done well and scooped up a good one. The simile is from fishing; the one caught is better than the rest of the fish in the sea.
Therefore the OP's phrase "Dr. Lahiri is no catch out of central casting" means to me that there was no element of any exceptional talent and that s/he was indeed, and disappointly, a run-of-the-mill extra.