Peel the beets and cut into 1/4'' slices. Process the bread in a food processor to make the crumbs, set aside. Cook the bacon until crisp, remove from pan and place on a paper towel. Discard all but 2 T of bacon fat, set aside. Return pan to medium heat, add breadcrumbs and thyme, and then saute for about a minute until crumbs are crisp. Crumble the bacon and add it to the pan. Remove from heat and reserve. In a large bowl, toss the beet slices with the bacon fat and salt. Arrange the slices in a casserole dish and bake in a preheated, 400 degree oven for appx. 40 minutes or until fork tender. Serve with feta crumbles on top of the beets, and then bacon crumbs sprinkled on top.