1) Using a vegetable peeler, remove the zest from 2 oranges in strips. Cut the strips lengthwise as thinly as possible until you have 2 tablespoons of thin slices. Reserve the thin slices and discard the remaining zest.
2) Using a sharp knife, remove the entire rind from the 6 oranges and cut them in half lengthwise. Cut each half crosswise into .5-cm slices to form half-moons. Remove the seeds.
3) Heat the oil in a 25-cm skillet over high heat. Add the rosemary to the skillet, cook for a few seconds, and then add the olives. Cook for 10 seconds or until the olives begin to absorb the rosemary-infused oil. Stir in the reserved 2 tablespoons of thinly sliced orange zest. Cook for a few seconds, then remove the skillet from the heat and allow the mixture to cool in the skillet.
4) Add the orange juice to a medium-sized bowl and pour in twice the amount of olive oil as there is juice. Whisk lightly until combined. Season, to taste, with salt and pepper.
5) Put the spinach in a large bowl. Add the reserved orange slices and pour in the olive-orange mixture from the skillet. Add the vinaigrette and toss gently to evenly coat the spinach. Season with salt and pepper.
6) Transfer the salad to a serving platter or individual bowls. Grate some ricotta salata over the top, and serve immediately.