How to Make It
In a small saucepan of boiling water, cook the lemon zest for 1 minute; drain. Repeat 2 more times. In the saucepan, combine the blanched lemon zest with the lemon juice, sugar and water and simmer over moderate heat until syrupy, about 8 minutes. Add the mango and simmer for 1 minute. Stir in the lemon thyme.
In a mini food processor, pulse the basil leaves with the olive oil, Parmesan, garlic and pine nuts until a sauce forms. Season the pesto with salt.
In a saucepan, simmer the cream over moderately low heat until reduced by one-fourth, about 4 minutes. Add the tapenade and simmer for 1 minute. Season lightly with salt.
In a large skillet, heat the olive oil until shimmering. Season the mackerel with cayenne, salt and pepper. Add the fillets to the skillet, skin side down, and cook over high heat until browned and crisp, about 4 minutes. Turn and cook just until done, about 2 minutes longer.
Spoon the olive cream onto 4 plates and top with the mackerel. Dollop the lemon-mango confit on each plate and spoon the pesto alongside. Serve at once.