Season the salmon lightly with kosher salt and pepper. Place the salmon in a vacuum seal bag and seal. If you don't have a vacuum sealer, choose another air removal method.
When the salmon is done, remove it from the water bath and place it on the prepared baking sheet. Spread the pesto over the top of the salmon. Sprinkle with the parmesan. Place it under the broiler for 1 minute, until cheese is melted.
Squeeze the lemon over the top of the salmon and serve.