Preheat the oven to 400°. Line a sheet pan with parchment and lay the salmon loin it. Season with salt and pepper. Lay lemon slices over the top. Cook for approximately 15 minutes or until salmon is cooked through and flakes apart.
Let salmon cool, then use a fork to break it up into flakes. Place in a large mixing bowl.
While the salmon is cooking. Wash produce and finely dice onion, garlic, celery, red bell pepper, and parsley.
Heat a small skillet on medium heat. Add 2 tablespoon of butter to the pan. Once the butter is melted, add onions, garlic, celery, and red bell pepper. Cook until vegetables are softened and onions are translucent. Then add parsley and capers and warm through. Add this mixture to the flaky salmon in the mixing bowl.
Add 2 eggs and bread crumbs to the salmon and vegetables in the mixing bowl. Mix thoroughly.
Warm a large skillet on medium heat. It will take 2-3 round of frying to make all of the salmon cakes. Add ⅓ of the vegetable oil to the hot pan.
Form patties into 3” by 1” patties and lay in the hot pan. Cook on for 3-4 minutes or until they are brown and begin to hold together. Gently turn and cook on the other side for 3-4 minutes and then transfer to a plate lined with paper towels. Do this until all of the batter is used up, adding more oil between rounds if needed.