i've done the hot sauce... never thought about mustard. Just sick of it to be honest so anything to maks the taste... even the texture is bugging me now.
rinse really well
heat up a skillet, some sweet onion, green onion, (bell peper is good to add too) toss the tuna in there, heat through, add some rice heat almost through and add some egg whites (1 per lg can) and cook through.