Preheat the grill to medium-high heat and spray with nonstick spray.
Cook the bacon in a skillet over medium heat until crisp. Remove to a paper towel lined plate
Add the shallots to the skillet and saute until tender. Stir in the mustard, vinegar and sugar and season with salt and pepper, to taste.
Brush the peaches with olive oil and season with salt and pepper. Grill until golden and has grill char marks, about 1 to 2 minutes on each side.
Add the spinach and the sliced red onion to a large serving bowl. Add the peaches, the vinaigrette and the chopped bacon. Toss and serve.