Instructions

Combine the first 5 ingredients in a jar or covered container; shake to mix well.
Put tuna in a food storage bag; add about 4 tablespoons of the mustard mixture.
Seal the bag and let marinate for about 20 minutes.
Brush the grill with olive oil and heat.
Remove the tuna from the marinade and pour the marinade in a small saucepan.
Bring marinade to a full boil; remove from heat and set aside.
Grill the tuna over high heat for about 2 to 3 minutes on each side, or until done as desired.
Drizzle with the hot marinade, if desired.