You can make any cookie/quickbread/cake recipe into a diet version by:
reduce the sugar by about half; most recipes make things way too sweet.
replace the fat with applesauce, peanut butter, avocado (or other fruit)
The texture will be a little different but the taste will be there. For cookies, you can replace all the fat. For quickbreads or cakes, keep 1/4 cup of oil and replace the rest with applesauce. The extra attraction of using applesauce or fruit is the natural sweetness means you can cut way back on the sugar as well.
Choose what you want to use based on the recipe. For cookies, a 50/50 combo of peanut butter and applesauce works well and the taste of peanut butter with choc chip cookies is pretty good. You won't get a thin crisp cookie, since how much a cookie spreads depends on the fat used. If you don't use any fat, there isn't any spreading so whatever shape the cookie is in when you put it in the oven is what you get.
For Quickbreads or cakes, the applesauce also makes for a very moist cake; best cornbread ever, for example. I used to be hesitant to try this, but have had such success that I take any recipe (like the Barefoot Contessa's carrot cake which is high sugar and high fat) and convert it. You need to keep a little oil or they won't raise sufficiently.
Sue