Dinner on Strand

There is the venerable Simpsons'-on-the -Strand, but that is not to our taste. For pre-theatre dinner we generally go to Côte Bistro at 17-21 Tavistock Street, a few blocks away.

http://www.cote-restaurants.co.uk/cote/restaurant/details/coventgarden

They have a very nice and reasonably-priced early menu, 2 or 3 courses for £12-14.

I eat a lot of Indian food when I'm in England. My favorite places close by there (<10 minute walk) are Dishoom and Punjab.

I don't know what you exactly mean by a nice dinner.

If it is posh, I don't do posh. If I were at the Adelphi, I'd probably either eat at the Wagamama at Covent Garden or something a little further away in either Wardour Street (Princi, Wahaca, or one of the others) or Charlotte Street (probably Wahaca). All of these will be open continuously from lunch...

My choice would probably be Busaba Eathai near Covent Garden ... If you prefer Leicester Square there's one there too. Busaba is my favourite Thai inspired food.

Not looking for a white glove dinner just a nice sit down place with great food

Assuming you like French "bistro" fare, I will repeat my suggestion of Côte. It is a sit-down place with individual tables ( not shared), nice food and wine, and you can reserve a table---which you should as they get busy in the pre-theatre hours. Take a look at their menu on the link above.

In that area, I like The Opera Tavern which has Mediterranean small plates, nice wines by the glass, takes reservations, and is open late so works for post theatre (my preference) as well as pre-theatre.
http://www.operatavern.co.uk

The Delauney is also relatively close to your theatre. It has Viennese food.

https://www.thedelaunay.com

The Criterion is a gorgeous restaurant with superb food - the Criterion Theatre is below it. Not cheap, but memorable.
If your play is on Thursday, Friday, or Saturday, another great place for dinner is the restaurant on top of the National Portrait Gallery. Great view, excellent food,
The Sherlock Holmes Pub is fun - not fancy. They have a Sherlock display on the 2nd floor above the pub. Lots of locals eating / drinking there.

You're not far from Chinatown, there's Rules on Maiden Lane and more pubs and restaurants than you could shake a stick at on and around Strand, Fleet Street and Aldwych. I like Temple Brewhouse on Essex Street.

I second Nigel's recommendation of the Covent Garden Wagamama. A bit further away from the theatre would be Zizzi in Bow Street or Carluccio in Garrick Street.

All these are chains, but to be honest in that area you have a choice of chains or tourist traps.

I just love this place, a cousin to the Wolseley and a 7 minute walk from your theater. https://www.thedelaunay.com/

Balthazar in Covent Garden does a prix fixe pre-theatre menu from 5-6:30 every evening. www.balthazarlondon.com

I liked it.

Cynthia, Thank you so much, we chose the top of the National Portrait Gallery and it was fantastic. The food, the service and the views were pretty amazing. Having the chance to get a window table and dining with Big Ben off in the distance is something most don't get to do everyday. Thanks again, your suggestion was just what we were looking for.

That's the difference in seeing the question through tourist eyes rather than local eyes.

The locals suggest easy inexpensive and close. You wanted a dinner view. We see the view all the time, so I didn't even think of it.

So glad you had a great time.