Sprinkle scallops with salt and pepper; dust with flour. Heat oil in large skillet over high heat. Add scallops; saute until brown and just cooked through, about 3 minutes per side. Remove skillet from heat. Using tongs, transfer scallops to platter. Add butter, lemon juice, 2 tablespoons water and mustard to skillet and scrape up browned bits. Place skillet over medium-low heat. Whisk until sauce simmers and thickens, about 2 minutes. Season sauce with salt and pepper; spoon over scallops.