Preheat oven to 425 degrees F.

Slice onion into thin strips. Mince garlic.

Using a square glass baking dish, lay in some of the onions, then the salmon fillets, then dot on butter, garlic, and the remaining onions. Sprinkle over the salt. Apply a foil lid tightly and bake for ~15 minutes, or until salmon reaches an internal temperature reaches 125-130 degrees F.

Remove from oven and let rest for 5 minutes before consuming with lemon juice squeezed atop.