Sprinkle the scallops with lemon juice. Season with salt and pepper to taste.
Whisk together the mustard, vinegar, olive oil, salt, pepper, and sugar.
In a pan, heat the butter, add the cherry tomatoes and scallops, and cook for 2-4 minutes. Let it cool.
In a bowl, combine the spinach, parsley, tomatoes, scallops, and vinaigrette. Mix well and distribute the salad evenly on plates.