A many years ago, when I was young and charming---oh...sorry--that's another thing entirely.. Back in the dark ages, around 1978 or so, when I got my first microwave oven, it came with a cookbook, and one of the recipes was for a microwave coffee cake. The cookbook is either packed up in a box somewhere, or long gone, but that coffee cake was about the only recipe we ever used--it was delicious..The book was coming unbound at that page.
I have been all over the place online, and cannot find any similar recipe, for a microwaved coffee cake in a standard 8x8 pan; all that comes up are single serving types baked in a mug.
The microwave was a GE model, and the cookbook was put out under their name, and no, nothing came up on their website, either.
You reminded me of how wonderful a nice, crumbly coffee cake could be. Seems they don't make that anymore. They just come up with these coffee buns that are lame in comparison. Good luck in your search and I hope you find the recipe you are looking for.