Start by combining the orange zest and juice with the balsamic vinegar, soy sauce, ginger, dry mustard, salt & pepper in a blender or food processor. Pulse until all the ingredients are well processed.
While the motor is running, slowly add the olive oil a little at a time. What you are doing is emulsifying the oil into the other ingredients. If you don't do it this way, the ingredients will separate.
Grill the steaks on your favorite grill to the doneness you like. Since these were not fresh, I cooked them all the way through so my girls would eat them.
You can store this marinade in the refrigerator in a clean container or freeze it for up to a week.
I only marinated the tuna for 30 minutes, and it was great. Imagine how much better it would have been if I had marinated for 3 hours?