Combine paprika, garlic powder and salt & pepper in a small dish, stir to combine and set aside.
Combine onion and pepper in a bowl, drizzle with olive oil and season with ½ of paprika seasoning blend. Reserve remaining seasoning for fish.
Cover a sheet pan with heavy duty foil big enough to create a “packet” for fish and peppers.
Place Salmon on foil lined sheet pan, drizzle with olive oil and remaining Paprika seasoning blend. Place seasoned onions and peppers on top of salmon, dot with butter.
Slice 1 lemon into rings and place on top of peppers and onions.
Seal foil at the top leaving room in pouch for steaming.
Cook in 375-degree oven until salmon is to desired doneness. 15-22 minutes.