Cook 2 tablespoons butter, 2 tablespoons olive oil, the onion, celery, red and yellow bell peppers, parsley, capers, hot sauce, Worcestershire sauce, 1/2 teaspoon salt, and 1/2 teaspoon pepper in a large sauté pan over medium heat until the vegetables are soft. Cool it to room temperature. In a large bowl mix mayonnaise, mustard, and eggs and vegetable mixture. Cover and chill for 20 minutes. Shape into patties. Heat 2-3 Tablespoons olive oil in a large sauté pan over medium heat. Add the salmon patties and fry for 3 to 4 minutes on each side, until browned. Top with fresh spinach and pickled red onions.

Combine vinegar, water, sugar, and salt in a medium bowl. Whisk together until sugar and salt is fully dissolved.

Place onion in a jar or bowl (Chef Santallana likes to use a mason jar). Pour vinegar mixture over the onions and let sit at room temperature for at least 1 hour if you’re in a rush. Preferably, cover jar or bowl and place in refrigerator for at least 1 day. Pickled onions will last for a few weeks stored in the refrigerator.