Preheat the oven to 425F.
Line a baking sheet with foil.
Wash cauliflower and remove any leaves.
Chop cauliflower into florets, discarding any thick stalks.
Cut the lemon in half lengthwise, then slice one half into thin slices. Remove any seeds.
Juice the remaining half of lemon, mix with olive oil and set aside.
Coarsely chop the olives.
On the baking sheet, spread the cauliflower into a single layer and toss with olive oil and lemon juice mixture.
Season to taste with salt and pepper.
Spread the lemon slices and olives over the cauliflower and toss again.
Roast in the oven for 12 to 14 minutes, stir halfway through baking. Florets should begin to brown a golden color.