National cake of the phillipines, Cassava cake, is very nice. Tastes like a cross between apple crumble & creme caramel & is "cakey". You do have to make sure you cook it right through though as uncooked cassava is dangerous. I don't have current recipe but you can find online.
One thing with gluten free flour. Assuming you are using a premade gluten-free flour like Dove's Farm - most are made predominantly from rice flour with a few other starches added. Rice flour basically just breaks down to sugar, so for a diabetic isn't great as it will raise blood sugar. That's why for a diabetic I would go for a ground almond cake, even with a small amount of sugar in it.
Just to say my DH has been Type 1 for 20 years, we have always been told that you can have a little things like cake as a treat, as long as you don't eat the whole cake in one go. You are not being inconsiderate by offering cake, just don't give a huge portion or have a lot of icing
Please don't try to make it with one of the sugar alternatives, they taste vile, and are probably not GF, as others have said a nice plain cake would be a treat, if I make a fruit cake I usually make something like a tea bread where you soak the fruit, I then reduce the amount of sugar by 1/3. We can't tell the difference.
What about an orange and ground almond cake? Not hard to do, nice and moist, a lovely orangey tang so less sugar can be used and doesn't really need icing. Recipes all over the place.
I have a gf recipe that uses beetroot, cocoa and dates with no added sugar if that’s any good. Or perhaps make a ‘sandwich cake’ using gf bread layered with yummy fillings? Decorate with toms, cucumber etc
As a pre diabetic trying to get healthy can I be controversial and suggest not making cake and showing you care in a different way? Go for a walk somewhere nice or do something else enjoyable that doesn’t involve food. Or make a tasty soup for a lunch date. Just an idea….
I’ve found a gluten free lemon drizzle recipe on the BBC Good Food site, for my nephew who is visiting next week. This might not suit a diabetic, though.
I agree, focus on the gluten free element and don’t add icing. My diabetic son will very rarely eat cake and if he does will have just a thin slice of whatever we are eating. You really don’t want to be adding artificial sweeteners as they can cause their own problems.
My advice would be to concentrate on the gluten-free element and just make an un-iced cake, perhaps a lemon sponge ( I do this for my diabetic OH ). If your friend is sensible they will no doubt restrict their consumption of the cake. Otherwise - google it!