Preheat the oven to 400 degrees F (204 degrees C). Line a baking sheet with foil or parchment paper.

In a pan over medium heat, heat the olive oil. Add the onion and saute for 7-10 minutes, until translucent and starting to brown. (or cook longer to caramelize if desired).

Add the garlic and saute for about 1 minute, until fragrant.

Meanwhile, in a medium bowl, whisk together the mayonnaise, fresh parsley, lemon juice, and Old Bay seasoning.

Stir in the sauteed onion and garlic mixture. Gently fold in the lump crab meat, without breaking up the lumps.

Place the salmon filet on the baking sheet. Season both sides with salt and pepper.

Arrange the crab mixture lengthwise down the middle of the salmon. Starting from the thinner edge of the filet, fold over the long way. If the fish doesn’t want to stay folded, secure the edge with toothpicks.

In a small bowl, whisk together the melted butter and lemon zest. Brush the lemon butter over the top of the salmon.

Bake for 16-18 minutes, until the fish flakes easily with a fork or the fish (not the filling) internal temperature reaches 130-140 degrees F, depending on how done you like your fish.

If desired, sprinkle the fish with additional fresh parsley. Cut crosswise to serve.