Salmon Croquettes

1 tablespoon extra-virgin olive oil,
1/4 cup minced red onion 
2 tablespoons minced red bell pepper 
2 tablespoons minced celery 
1 tablespoon capers 
1 1/4 pounds fresh  salmon, coarsely chopped 
1/4 cup panko bread crumbs 
1 teaspoon Dijon mustard 
2 pinch seafood seasoning (such as Old Bay®) 
1 tablespoon panko bread crumbs, or to taste
2 tablespoons olive oil, or as needed 

1. Heat extra virgin olive oil in a skillet over medium heat. Cook and stir onion, red pepper, celery, in hot oil until onion is soft and translucent, about 5 minutes. Add capers; cook and stir until fragrant, about 2 minutes. Remove from heat and cool to room temperature. 
2. Grind salmon, then add onion mixture, 1/4 cup bread crumbs, , mustard, seafood seasoning, together in a bowl until well-mixed. Cover the bowl with plastic wrap and refrigerate until firmed and chilled, 1 to 2 hours. 
3. Form salmon mixture into four 1-inch thick croquette; sprinkle remaining panko bread crumbs over each patty.  Divide croquette into 4 for bite sized pieces
4. Heat olive oil in a skillet over medium-heat. Cook croquette in hot oil until golden and cooked through, 3 to 4 minutes per side.