In a large bowl whisk together the cornmeal, red onion, and baking powder. Make a well (hole) in the center and pour in the buttermilk and egg.
Stir the batter with a fork until well combined. Carefully fold in the corn and the trout.
Heat a thin layer of olive oil over medium heat in a large cast iron skillet. Drop in equal sized spoonfuls of batter (I used an ice cream scoop and got 8 fritters) and flatten with a spatula. Cook in batches until golden brown, 3 to 5 minutes per side. (See notes about cooking temperature.)
Sprinkle with salt and pepper and set aside.
For the Buttermilk Dill Dressing
Blend together the sour cream, buttermilk, lemon juice, dill, and garlic until smooth.
Add lettuce or spinach to large bowls, top with the fritters, dressing, additional diced red onion, salt & pepper, and serve.
If your pan is too hot they will get brown on the outside before they are cooked all the way through the middle, so be sure to cut one open to check your temperature setting!