Preheat the oven to 375°. Toast the pecans on a baking sheet for 5 minutes. Transfer the nuts to a bowl, toss with the butter, honey, Parmesan and a generous pinch each of salt and pepper, then spread on the sheet and bake for 4 minutes, or until golden. Let cool.
In a small bowl, whisk the lemon juice with the shallots and mustard. Whisk in the oil and season with salt and pepper.
With a sharp knife, peel the oranges, removing all of the bitter white pith. Halve the oranges lengthwise, then slice crosswise 1/4 inch thick.
In a large bowl, toss the spinach with the dressing, olives, pecans and oranges and serve at once.