Spinach is always a great add-in, too! I always switch around my leafy greens weekly, so one week it's arugula, the next my be spinach, then some kale. They each have a different flavor and texture to jazz up your dishes. The good thing about the sauce is you can either leave it off or switch it up if you don't enjoy mustard. You could probably sub tomatoes or tomato paste if that's more your speed perhaps?