Blood oranges, if they're around, are beautiful
here, but navels or even grapefruit work well.
750 gmpiece skinless yellowfin tuna Olive oil, for brushing and drizzling3 tspfennel seeds, crushed with a mortar and pestle3blood oranges, rind of 1 finely grated, all peeled, thinly sliced and seeds removed½head of radicchio, torn1fennel bulb, shaved on a mandolin, fronds reserved1large golden shallot, thinly sliced on a mandolin1 cup (firmly packed)basil, plus extra to serveBlack olive dressing100 mlextra-virgin olive oil50 gmblack olives, such as Gaeta, pitted2 tbspred wine vinegar, or to taste1small garlic clove, crushed½long red chilli, coarsely chopped Finely grated rind of ½ blood orange and juice of 12 tspbrown sugar
For black olive dressing, pound or process ingredients in a blender until combined and season to taste.
Heat a barbecue or char-grill pan to high. Brush tuna with oil, press fennel seeds all over fish and season to taste. Drizzle with oil and grill, turning occasionally, until charred on the outside and rare inside (4-5 minutes). Rest for a minute, then thickly slice.
Combine blood orange, radicchio, fennel, shallot and basil in a bowl. Dress with half the black olive dressing, toss to combine and season to taste. Serve salad with tuna and scatter with extra basil and fennel fronds, and drizzle with remaining dressing.