oh gosh, i feel your pain..one of my kids did the same thing but would only like a food for about 1 meal and if i was lucky, one whole day
i was able to finally find something she will consistently eat but it was a challenge trying to find something...and expensive!! and actually, i am worried she is getting bored again lol
i also tried adding in all the suggested items (cheese, parmesan cheese, yogurt, egg, chicken, etc) and NOTHING worked with her for more than one meal
i hope you find a solution quick as i understand how frustrating this is