There’s lots of posts with good advice about eating while traveling. Just search for those terms. You might be in luck travelling in Africa. Isn’t Ethiopian food centered around injeera, which is a Teff flour bread?
Who are you wanting the physician to write a note to? The airlines? Your workplace? Who is compelling you to travel? Candida overgrowth is so poorly understood I would not expect it to stand up as a medical excuse, though there is never any harm in asking your alternative practitioner and/or whatever entity you are petitioning.