In a large bowl, combine the salmon, onion, horseradish, mustard, parsley, eggs, 1/2 teaspoon of the salt, and the pepper. Using a fork, mash together all the ingredients until the mixture comes together in a mass that you can shape into balls. Form 12 balls. Each one will be about the size of a small lemon. Flatten into cakes approximately 2 1/2 inches in diameter. Set aside in a single layer on aluminum foil or waxed paper.

Preheat an oven to 300°.

Combine 1 1/2 tablespoons of the oil and 1 1/2 tablespoons of the butter in a skillet large enough to hold half of the cakes at one time. Place over medium heat. Meanwhile, sprinkle half of the bread crumbs onto another sheet of foil or waxed paper. Press both sides of 6 of the cakes into the crumbs. When the butter has melted, carefully slip the crumbed cakes into the skillet. Cook for about 2 minutes on each side until crispy brown. Remove and set aside to drain on absorbent towels or paper, then place in the oven to keep warm. Add the remaining 1 1/2 tablespoons oil and 1 1/2 tablespoons of the butter to the skillet, coat the remaining cakes with the remaining crumbs in the same manner, and then cook them as you did the first batch. Again, drain on absorbent towels and keep warm.

In a large skillet or wok over medium heat, melt the remaining 1 tablespoon butter. Add the greens, cover, and cook for 30 to 40 seconds. Uncover, stir, re-cover, and cook until the greens have just wilted but still retain their color, another 30 seconds. Sprinkle with the remaining 1/2 teaspoon salt, increase the heat to high, and pour on the lemon juice. Stir and cook for another 15 to 20 seconds.

To serve, arrange a bed of the wilted greens on a platter or individual plates and top with the salmon cakes.