Cut the lobster meat into ½-inch dice. Place the cucumber in a colander for at least 5 minutes to drain the excess liquid. Combine the lobster, cucumber, and Mayonnaise. If the salad is to be served within the hour, add the scallions. If not, add them 30 minutes before serving. Season with salt if needed and pepper. Cover with plastic wrap and chill for at least 30 minutes before serving.