The whole thing sounded bland, so in addition to the optional tomato, I added 1 big clove garlic, a few dashes each of parsley, marjoram, and Tabasco. I pulsed everything in the food processor to make it easier, and it turned out fine. Rather than drizzling with olive oil, I sprinkled the tops with panko before baking. I also sprinkled on a little grated parmesan during the last 10 minutes.
It STILL wasn't very flavorful, and the whole thing had a funny metallic taste to it despite using a good brand of tuna. I won't be making it again.