Preheat oven to 400°F. Rinse the salmon well under cold running water & sprinkle inside the cavity with salt & pepper.
Stuff with half of the red onion slices, half of the lemon slices, & all of the parsley. Lay the salmon on enough aluminum foil wrap to enclose fully.
Rub both sides with olive oil, sprinkle with salt, pepper, & thyme. Scatter the remaining onion & lemon slices on top & seal foil tightly around salmon.
Bake on baking sheet 40-45 minutes, adjusting time for size of salmon. Cool salmon in foil on cooling rack, then remove onion & lemon slices.
Remove skin if desired & served baked salmon at room temperature.
Recipe by Food Askew at http://foodaskew.net/2012/01/alaskan-baked-salmon/