Salmon with Brown Sugar and Mustard Glaze

INGREDIENTS

• 1 tablespoon extra-virgin olive oil
• 1 large shallot, minced
• 1/4 cup red-wine vinegar
• 1/4 cup whole-grain mustard
• 1/4 cup packed dark-brown sugar
• Coarse salt and ground pepper
• 1 side salmon (about 3 pounds), skin removed, cut into 8 fillets
• 1 bunch watercress (about 3/4 pound), thick stems trimmed
• 1 lemon, cut into wedges, for serving