In a medium bowl, whisk egg and milk together. Stir in cornmeal, flour, salt, and baking powder, and fold in green onions and corn.
Set a large non-stick frying pan or a large griddle over medium heat, and add 1 tablespoon oil. Scoop ¼-cup portions of batter into pan. Cook, turning once, until puffed and golden brown, about 6 minutes total. As the cooked cakes come off the griddle, set them on a cooking rack.
Repeat process with remaining batter, adding more oil as necessary to the pan.
Place tuna in a medium bowl, and break apart any large chunks with a fork.
Place the onion slices in a colander and rinse with cold water. Rinsing the onion will remove its stinging bite and mellow the taste, making the onion sweeter. It will also help to make your eyes not water as the sulfates that irritate your eyes get rinsed away.
Add the onion, tomato, and avocado to the bowl with the tuna.
In a separate small bowl, mix olive oil, lime juice, cilantro, salt, pepper, and cayenne pepper. Pour dressing over salad, and mix gently.
To Serve: place two corn cakes on a plate, and scoop some summer salad on top. Garnish with chopped green onion, cilantro, or sour cream, if desired. Enjoy!
Makes about 10 cakes, more than you need for the salad recipe.