Line a rimmed baking sheet with a piece of aluminum foil big enough to encase salmon. Lightly coat the foil with baking spay.
Arrange 2-3 sprigs of the rosemary down the middle.
Cut one lemon into thin slices and arrange half the slices down the middle with the rosemary.
Place the salmon on top – skin side down if you opted for skin on.
Drizzle the salmon with the olive oil and sprinkle with the salt and pepper. Rub to coat, then scatter the garlic over the top.
Lay the remaining rosemary and lemon slices on top of the salmon.
Juice the second lemon, then pour the juice over the top.
Fold the sides of the aluminum foil up and over the top of the salmon until it is completely enclosed. Make sure there is room for air circulation inside the packet.
Bake the salmon for 15-20 minutes, until the salmon is almost completely cooked through at the thickest part. (Cooking times vary depending on the thickness of the salmon.)
Remove the salmon from the oven and carefully open the foil so that the top of the fish is completely uncovered.
Change the oven setting to broil, then return the fish to the oven and broil for 3 minutes. (Watch closely so garlic doesn’t burn.)
To serve, cut the salmon into portions. Portion amounts vary depending on how big your salmon is – you can also do this with pre-portioned filets.