Season both sides with salt. Transfer to the fridge to cure for 30 minutes.
Pat the salmon dry again, wiping off most of the salt. Season with pepper.
Arrange the salmon, skin-side-down, on the prepared baking sheet.
Whisk together the Dijon mustard and 2 tablespoons of the maple syrup.
Brush the mustard syrup evenly over the tops of the fillets.
Combine the pecans, breadcrumbs, melted butter, and thyme in a bowl.
Press the mixture firmly onto the top of each fillet.
Bake the salmon for 15 to 18 minutes, until it flakes easily with a fork and the crust is golden brown. Tent loosely with foil halfway through if the crust browns too quickly.
Whisk together the remaining 1 tablespoon maple syrup and the lemon juice.