Slice broccolini lengthways into long strips; thicker stalks can be quartered, while thinner ones can be halved. Toss on a lined baking tray in a little olive oil and roast for 20 minutes or until edges are starting to shrivel, check the tray after 10 minutes and turn any stalks that are browning quickly. Roast 6 or 8 unpeeled garlic cloves alongside the broccolini. Remove from oven and allow to cool to make handling less painful.
Prepare a plain pizza base, and bake for 15 minutes at 220C, remove from oven and cool slightly.
Sprinkle pizza base with a generous layer of grated mozzarella cheese. Squeeze garlic from skins and distribute over cheese. Arrange broccolini stalks top to toe along length of pizza, then dot with a handful each of walnut halves and black olives.
Bake for another 10 to 15 minutes or until walnuts are crisped and cheese is bubbling.