Preheat oven to 80°C (176°F). Heat the baking sheet inside the oven and lightly grease it.
Pat the salmon fillet dry and place skin-side down on the warmed baking sheet. Season with salt and pepper. Rinse and pat dry the basil. Remove leaves from 5 basil stems, chop finely, and spread over the salmon. Return the baking sheet to the oven and cook for 40 minutes.
Rinse the lemons with hot water and pat dry. Use a peeler to thinly peel the lemon zest. Squeeze the juice from the lemons. Pluck the leaves from the remaining 1 basil stem.
Check if the salmon is cooked through by piercing with a fork — it should be very juicy. Transfer the salmon fillet to a plate, drizzle with olive oil and lemon juice, and top with lemon zest and basil leaves. Serve lukewarm with baguette, green salad, and dry white wine. Also works well on a cold buffet.