Preheat oven to 500ºF.
Put the turnips in a bowl with the bacon, bay leaves and cinnamon. Add the oil, season with salt and pepper and toss everything together.
Put an empty roasting pan into the oven. The pan should be large enough to hold everything in a single layer with plenty of space. Let heat for 5 minutes.
After 5 minutes, carefully remove the hot pan from the oven and add the turnips, cut-side down, with the bacon, bay leaves and cinnamon, leaving space between the individual slices.
Roast the turnips until golden brown on the contact side, about 10 minutes. Flip the turnips so the seared side faces up.
Remove the lardons from the pan to prevent them from burning. Add the dates to the pan, turning them about to cover with fat.
Return the pan in the oven and roast until the turnips are tender, another 6 minutes or so. The dates should be just starting to dry out a bit and get crispy.
Toss with the zest, thyme and lemon juice and transfer to a platter, leaving the bay leaves and cinnamon behind.
Serve warm.
