Food here is excellent, but eating well involves some counterintuitive advice.
For one thing, there are few “undiscovered gems” along the roadways. It is just not a thing here, and several Sri Lanka residents have confirmed this to me (one person suggested there used to be lots of them, but they have faded). During my extensive road travels, I saw many many closed, empty, or otherwise deserted roadside restaurants. The open ones had few or no customers. So don’t put a lot of time into searching for them. You will do just fine eating at the obvious restaurants, including hotel restaurants.
Often breakfast is the best meal, as you can sample hoppers and string hoppers. If they will cook a hopper for you with an egg (and spices) inside, do that. Think of it as a spongy carbohydrate turned into a kind of crepe. The egg inside should not be overdone, but the woman cooking it for you has done this 7,834 times before, so probably it will be just right.
When you get string hoppers, it is all a matter of composition. Put the right spices, sauces, and sambals on top. Ask for assistance. The quality of the string hoppers varies only marginally, it is really all about your skills at composition and at asking for aid.
Hoppers and string hoppers are pretty much always very good. You want to keep on ordering them. And yes, food in Sri Lanka is somewhat of an exercise in repeated monotony, but it is a very appealing repeated monotony.
Vegetables in Sri Lanka are first-rate, and if you visit the vegetable markets in and near Dambulla you will come away impressed. If you are served just ordinary broccoli or cauliflower, without spice or garnish, it will be as good as anywhere.
The best vegetable to eat Sri Lankan style is the green beans. Never turn them down. Overall, Sri Lanka is one of the very best countries for vegetarians or vegans. You’ll see many other kinds of curry, such as with jackfruit or manioc, and they are not bad, but once you have tried them you will be returning to the green beans.
The lentils are consistently superb, arguably better overall than in India, though in fewer styles. Keep on ordering them.
Thou shalt not refuse any curry served with cashews in it.
If you are at a buffet, sample any item that has a small green leaf in the sauce. Sample any item with an unusual name, with “tempered cowpeas” being one but not the only example.
Beware of buffets designed for Russian or Chinese package tourists, though usually there will be hoppers or string hoppers somewhere to be had.
Coconut roti is a wonderful snack, but you should not eat too many of them, either at once or across the course of a lifetime.
There is the usual array of tropical fruits, high in quality, though to be frank most of them bore me at this point.
Both pork and bacon are excellent (and common) in Sri Lanka. The pork is much better than the beef. So far I’ve had better luck with shrimp than with fish, though I don’t feel I’ve cracked the cultural codes yet for seafood. Some love Sri Lankan crab, but I haven’t had the chance to explore that direction.
Western-style baked goods are by no means a total disaster here, and it is not a mistake to try them. The high quality is supposed to stem from the earlier Portuguese influence, at least if you can believe llama Chat.
Aqua Forte, in Galle, is a Michelin star-quality Italian restaurant with affordable prices. The chef is from Trentino. The cured raw fish with pistachios is one of the best courses I’ve had in years.
In Colombo, Monsoon is a good Asian fusion place, get the beef rendang. Shang Palace is a good Chinese restaurant.
In sum, you can eat very well here at great prices and booking doesn’t ever seem to be a problem. You do need to be willing to double and triple down on some items, but don’t worry — you’ll like them!
Addendum: The perceptive reader will note I have covered only the food of southern Sri Lanka. That is also the part of the country — by far — that you are most likely to visit.