Using FRESH salmon fillets, place skin side down on a plate to apply marinade. If you have large fillets, you may prepare two fillets and slice serving portions AFTER cooking.
In a small bowl, combine pepper, onion powder, garlic powder, celery salt, and paprika. Stir together to combine.
Squeeze 1/2 fresh lemon over fillets then sprinkle seasoning mixture over fillets. Let sit for at least five minutes while oil heats.
Heat olive oil in a large heavy skillet over medium heat for 3-5 minutes (a cast iron skillet works best).
Place marinated fillets flesh side down into hot oil, then turn heat up to high/medium-high, depending on your stove settings. (Oil should be popping/bubbling when fillets are placed into oiled skillet). Cook for 3-4 minutes (flesh side should be browned), then turn fillets over. Place 1/2 tablespoon jarred capers over each fillet (or 1 tablespoon each if large fillets) and sprinkle lightly with pepper. Lower heat to medium and continue to cook for approximately 5 minutes or until fish flakes easily. (Do not overcook, salmon cooks quickly).
Remove salmon from skillet and garnish with a lemon slice. (Cut slice halfway to center and twist for the effect shown in the picture). Garnish plate with more capers if desired.