hey mel, how about coring, skinning, and slicing them into 1/4 inch disks, then frying them in 1/2 stick of butter until just beginning to become soft with slightly thinner sliced onions. layer in the bottom of a baking dish, and pre-heat oven to 350.
next, in the same frying pan brown 2 pork tenderloins on all sides in evoo and butter, place pork atop the onions/apples, deglaze the pan with some white wine or water or chicken stock, pour over pork/onions/apples.
finally, spread a good layer of wholegrain dijon mustard over the pork loins, sprinkle with fennel seeds and press them into the mustard.
bake uncovered for 20 - 40 minutes (depending on the size of the tenderloins), or until the pork is 145 degrees in the center.
remove and slice tenderloins on a bias, plate onions and apples, place pork on top. reduce the remaining liquid a little and drizzle over top.