Makes me wonder where you live as wherever I've gone on my travels, even if it's a place where vegetarian food is very hard to find (looking at you France. And rural Scotland. But especially France), they always remember the protein. I've never ended up with a basic salad, honest. In England virtually everywhere has at least two vegetarian options, and funnily enough you're more likely to worry about not getting enough of your five-a-day from them than your dose of protein. America was the same fort me. In England the only problems come at football grounds, so I either look for a gastropub beforehand or take packed lunch.
Now I don't go to chains and it rarely even registers to me to visit one as an option, but anywhere worth their salt will find a cheese to go with that salad if you specify, and similar. If that sounds like an anal thing to do please be assured that a lot of us ask for extra toppings, or for xyz to be omitted from a meal we order. I know that's extremely plain but you might be stuck for choice. Usually places with more vegetarian options tend to do higher quality food anyway, and I hear that feedback from meat eaters.