Whisk the dressing ingredients together and set aside.
Cut the core from the radicchio then separate the leaves. Wash and dry carefully. Tear into bite-size pieces and place in a large bowl. Prepare the iceberg lettuce in the same way. Mix with the tomato slices, most of the spring onions (reserving some for garnish) and sunflower seeds (if used).
Toss with half the dressing, add more seasoning if liked, then divide between four plates.
Cut the rind from the cheese then slice into eight. Place two pieces on each plate, drizzle over the last of the dressing and scatter over the remaining spring onion shreds.