Wife had one years ago now, she did ok, was Pizza which is very popular, she got taught by an old Italian who was very good, she wasn't bad. Italians liked her food though could never get a gas oven hot enough without spending a lot.
We would have made a traditional oven but then work took me away from Thailand.
Someone else mentioned but I'll add here too, her successful part which others mentioned was doing delivery, and marketing delivery to the local government offices during the day. We lived in a large town with a big government population
Schools also she'd deliver too but that had to be carefully managed, a few schools banned deliveries so she did a deal with the local catholic school to do delivery just 2 days a week an the school collected the orders, phoned them through, and she did a bulk delivery with a 15% donation to the school. As it was a bulk order that came at 11 am it gave her time to use oven etc when not competing for her own customers hence the bulk discount. Plus 25 pizzas in a single order is bloody good.
She tried to work on the 30% rule, 30% for rent and utilities, 30% for cost of goods, 30% labour. 10% profit
Labour you must include your own wages, if you don't you end up hating the business.
In reality it ended up with rent and labor being a bit less than 30% each and her profit being about 25%.
People used to say impossible to make pizzas for the price she did, arounf the 100baht mark 7 years ago, but it was easy to source good produce.
As mentioned by others, she also had some thai food and also burgers, lasagna, and some spaghetti
"Restaurants are owned by the landlord" a good mate of mine says, he had two famous restaurants and now owns the buildings not the restaurants.
My mate noted as he rented places, as he got more successful, so did the rent, was always chasing his tail. Ended up buying the building and selling the restaurant and making more with less stress.
Wife got lucky, the landlord had a pub and the space beside it they struggled to get going as a restaurant. So with a good cheap restaurant with pub style food the landlords main business improved.
Ironically her sister, niece and two of our kids are all into hospitality with focus on restaurants.
Our son is still in school and has a part time burger stand using his mums recipes, taught to her by a drunk Englishman who wanted a "real" burger a decade ago.
The recipe is so popular here in Oz he makes about $800 profit working on a 50% gross profit margin.
Not bad for a 16 year old!
Recipe is super simple, and that's the key to his success, he even advertises, "No Aioli" Aioli being flavoured mayonnaise, YUCK!
His sister works in a major city hotel, hasn't finished her studies but the head chef only allows her to manage ordering and special food preparations over more seasoned staff in the hotel.
It's a tough business. For that $800 from 4 hours of trading there is 8 hours of prep and 4 hours of clean up that goes with it. Still great money but if you have a day to day place it's a love of the job and people.
It's tough times, we thought about having a part of the place to serve drinks to the expat community but realized quickly they are fickle and don't actually spend that much. She then found the right local cliental and they became much better customers.
I know not recent experience but maybe chasing some catering as we did and my son does now might work and fill in the gaps,
All the best!