Cut the spinach leaves from the stalks and shred finely. Cut the rind from the bacon and slice into thin strips. Fry the bacon lightly for 2 or 3 minutes and drain on absorbent paper. Toss the spinach, bacon, mushrooms and snow peas together in a salad bowl. Add capers and toss in well.
Place the mayonnaise, orange juice and vinegar in a jar with a lid and shake well. The resultant mixture should be the consistency of a good gravy. Add to salad and toss well. Sprinkle with chopped chives.