Take a look at the kitchen set by Embroidery Garden. I have made several oven door towels by cutting the towel in half and using her ITH kitchen towel topper. I do find that the non terry towels work best as the terry is very thick.
Designs by Ju Ju has a great one. I made a bunch up as Christmas Gifts
Embroidery Weekly has some. I made one called Summer Towel Topper and it turned out beautifully. Hugs. Nan
I have some from Emblibrary. Search towel toppers
Any of them that don't have the slit as part of the design could be used - just put the half towel down along the bottom edge (on top of the hoop) before you start sewing that section so it would be secured in when you put on the back. I have seen some that are designed that way I just can remember where! I will come back if I figure it out.
I am not sure exactly what you mean with the slit. This one has a piece of elastic on the back where the towel is slipped through and the design is from Emblibrary