I have ADD, was on a heavy dose of Vyvanse / Elvanse for many years. Like you I decided to experiment going natural, trying to make various lifestyle changes e.g., eat healthier and exercise. Then I learnt about fasting. I would say that doing intermittent fasting, 20–4, eating in the evening has been beneficial to me, as I seem to be more motivated and able to concentrate throughout the day. I would also add that cold showers on the coldest setting for 4 mins every day in the morning are also making a huge difference. I couldn’t have ever imagined doing them as the cold water was, and often still is, the last thing I want to feel but I never regret it and always feel more motivated, focused and better in mood. Look up ‘cold therapy’ or ‘cold showers’ on YouTube if you’re interested to find out more.
I’m an unmedicated ADHDer and I wish I have your problem. I’d continue with OMAD if I were you, and keto if you can tolerate it (I’ve read that keto is good for us ADHDers). This way you can be safely on medication, lose weight, save money, don’t have dishes to wash, and have the time to pursue other things instead of worrying about food, food prep, and clean up! Freedom is bliss!