Center rack in oven. Preheat oven to 375 degrees F.

 

Drain tuna and place in a bowl, flake into small pieces with a fork. Stir in olives, if using. Cover and refrigerate.

 

Prick outside of potatoes with fork, to allow steam to escape. Bake until tender, 1 to 1-1/4 hours. Remove from oven, wrap with paper towels; set aside until cool enough to handle.

 

Increase oven to 500 degrees F. Cut potatoes in half, lengthwise. Scoop out flesh, leaving a 1/4-inch shell; brush both sides of shells with olive oil. Arrange on a large baking sheet; bake 4 to 5 minutes, until crisp.

 

Carefully remove baking sheet from oven. Spread each potato with 1 Tbsp pizza sauce, then sprinkle with flaked tuna and shredded cheese. Return to oven for 1 to 2 minutes, until bubbly and golden.