Season the flour with salt and pepper, and dredge the salmon steaks on both sides, patting off any excess flour mixture.
In a deep skillet, heat half the olive oil until bubbling. Brown salmon pieces on both sides over high heat. Remove to a plate and keep warm.
Add the onion and the remaining oil to the pan, and cook over medium heat until lightly browned. Add the apple slices, sugar and fennel. Cook until lightly browned, about 3 to 5 minutes. Add the broth and cider; heat to a simmer.
Return the salmon to the pan along with any juices that have collected on the plate. Cover and simmer for 8 to 10 minutes, until the salmon flakes when lightly pressed.
Lift the fish from the pan with a slotted spatula and place on a platter. Surround with the apples and fennel.
If the liquid in the pan is too thin, reduce for several minutes to thicken. Add the lemon juice and pour over the fish.