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. Using a sharp knife, remove the entire rind from the 6 oranges and cut them lengthwise in half. Cut each half crosswise into 1/4-inch slices to form half-moons. Remove the seeds.
Heat the oil in a 10-inch 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.
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.
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. Transfer the salad to a serving platter or individual bowls. Grate some ricotta salata over the top, and serve immediately.