I have about 6 hours in TXL between flights (with only light hand baggage). I intend to take the TXL bus or similar towards the Brandenburg Gate area or another central place.

I will need to eat lunch. I eat most anything. I am aware that Berlin is known for Döner, sausage, and beer

I welcome any suggestions for lunch in central Berlin.

Italian - Bocca di Bacco on Friedrichstrasse
German see and be seen - Borchart, just around the corner
Fish - Fischers Fritz, inside the Regent Hotel on Charlottenstrasse
Chinese - Good Friends in Charlottenburg
German (again) - Aigner on the Gendarmenmarkt, next to the Sofitel (best Wiener Schnitzel)

Just a few thoughts...

Those aren't bad suggestions but not exactly the most 'Berlin' lunch. Get a Currywurst with Pommes and you'll save money and get a very specific taste of Berlin instead .

You can even have that at TXL, in the Ess-Bahn, a converted former train car. But seriously, Currywurst is pretty disgusting. A good sausage ruined by ketchup flavoured with mild curry powder.

At least it is a good sausage and not Tesco's with "contains at least 10% of pork" in the fine print Curry Wurst is a "you need to eat it at least once in a lifetime" (probably like F&C with salt and vinegar in Brighton)

My recommendation would be to buy a day ticket Berlin zones AB for € 6,90 then get on bus X9 outside the terminal. Stay on it until the last stop (Zoologischer Garten) it's a 15 min ride at that time of day.

Then go one stop on either bus 100 or 200 (they both start at Zoologischer Garten).

Get off and cross the road and go up to the the 10th floor (express lift) of the 25 hours Hotel. Then decide on either Monkey Bar (turn right out of lift) or Neni's (turn left out of lift). In either place you will be sitting overlooking the zoo for lunch with good aerial views of Berlin. My choice would be Neni's

After lunch get back on the 100 bus and stay on that until Alexanderplatz (last stop) from where you can get the TXL bus back to the airport. The great thing about the 100 bus is that it basically goes along past all the sights in Berlin, following the route of the hop-on-hop-off buses which are much more expensive. Your day ticket will give you unlimited travel on public transport in Berlin.