Make the Dressing: Whisk the olive oil, fresh orange juice, honey, wholegrain mustard, apple cider vinegar, salt, and pepper together until well combined, then set aside until needed.
Build the Salad Base: Arrange the chopped iceberg lettuce, sliced cherry tomatoes, and finely sliced red onion on a large serving platter.
Dress the Vegetables: Pour some of the prepared dressing over the lettuce, tomatoes, and onion, then gently mix everything together so the vegetables are lightly coated.
Prepare the Halloumi: Thinly slice the halloumi, then cut the slices into bite-size pieces.
Fry the Halloumi: Heat a large non-stick frying pan and cook the halloumi for a few minutes on each side, turning as needed, until the pieces are golden.
Add the Avocado and Halloumi: Chop the ripe avocado and arrange it over the salad base along with the warm, golden halloumi.
Finish with Basil and Dressing: Scatter the chopped fresh basil over the salad, then drizzle with the remaining dressing just before serving.