In a small frying pan fry the bacon until crisp. Meanwhile wash the spinach and set aside.
In a large bowl mix together the mustard, pepper and the olive oil. When the bacon is done add half the bacon to the mix and most of the bacon rendering.
Add the salad and mix well, taste and add salt if need be.
Add the remaining bacon to the salad and serve.
The salad leaves need to be well coated. Add more mustard if need to