Empty 4 cans of tuna into a large strainer over the sink, and let them drain while you prepare the following ingredients.
Sauté onions in olive oil for about 8 minutes in a sauté pan, until translucent. Set aside and let cool.
While the onions are cooking, in a large mixing bowl, add Greek yogurt, lemon juice, salt and pepper and whisk till combined. Then add cilantro and peppers to the mixture.
If you are freezing the cakes, leave them on a cookie sheet and place them in the freezer for a few hours. Once they have firmed up you can transfer them to a resealable storage bag. When you want to cook them, place them back on a baking sheet while still frozen, and allow them to thaw in the fridge for at least 4-5 hours. Then proceed with baking per the instructions.
For an extra spicy kick add a tablespoon or two of Sriracha sauce to the mixture before forming the cakes.