I always start by preheating my oven to 375°F so it's fully heated by the time the salmon goes in. A properly preheated oven matters here since the first bake is short. While it heats up, I use the time to line my baking sheet with parchment paper, which makes cleanup so much easier later.
I place the salmon fillet on the parchment-lined baking sheet, then coat it with the oil and a pinch of sea salt. I like to rub the oil in gently so it covers the whole surface. This light coating helps the salmon stay moist during that first round of baking and gives it a nice base flavor.
I slide the salmon into the oven and bake it for 10 minutes at 375°F. This first stage gently cooks the fish through without drying it out. I use this time to make the basil butter sauce, so nothing goes to waste.
While the salmon bakes, I mix the melted butter with lemon juice, chopped basil, salt, and pepper in a small bowl. I like to taste it here and adjust the seasoning since this sauce is what carries most of the flavor. It should smell bright and buttery at the same time.
Once the salmon has baked for 10 minutes, I pull it out and spoon the basil butter mixture generously over the top. Then I layer on the lemon slices, which add flavor as they roast and also make the dish look really pretty once it's done.
I finish the salmon under the broiler on high for 5 to 6 minutes, watching closely so it doesn't overcook. The salmon is done when it turns from that shiny, reddish color to an opaque pink and starts to flake easily with a fork. Every oven runs a little different, so I always check a minute or two early the first time I make this.