In a small frying pan over medium-high heat, cook pancetta, stirring often, until crisp, 2 to 3 minutes. Transfer to a paper towel to drain.
Discard all but 1/2 tbsp. fat from pan. Add shallot and stir over medium-high heat until soft, 1 to 2 minutes. Remove from heat and whisk in oil, vinegar, mustard, and thyme. Season with salt and pepper.
Put spinach and sliced pear in a large bowl and gently toss with dressing. Arrange salad on plates. Crumble goat cheese on top and sprinkle with pancetta.
Note: Nutritional analysis is per 1 1/2-cup serving.