Preheat oven to 325 degrees. Spread pumpkin seeds out on a baking sheet and drizzle with oil. Toss well and sprinkle with coarse sea salt. Toss again. Place pan in oven and roast 20 to 30 minutes until pumpkin seeds are light brown.. Remove from oven and let cool.
In a small bowl, whisk together lime juice, mustard, fine salt and fresh pepper. Slowly drizzle in olive oil while whisking so as to form an emulsion. Peel pears, cut each into quarters lengthwise, cut out cores, and halve each quarter lengthwise. Place the pears in a small bowl and drizzle on 2 tablespoons dressing to keep from turning color.
When ready to serve, toss watercress with remaining vinaigrette and divide between 8 plates. Place 4 wedges of pear on each plate and sprinkle generous amount of roasted pumpkin seeds over.