Using a mandoline, slice the fennel into thin shavings.
Cut the bottom and top off of the grapefruit. Using a knife, cut the peel off of the sides, following the curve of the grapefruit and being careful only to cut away the peel and bitter pith. Hold the fruit in 1 hand over a bowl and cut the flesh of the grapefruit away from the membrane to release a wedge. Repeat until all segments are released.
In a large saute pan over medium heat coat with extra-virgin olive oil and add the fennel. Season with salt and saute for 1 to 2 minutes or until the fennel is warm and coated with the oil.
Remove from heat. Toss in the grapefruit segments, olive slivers and juice and sprinkle with the fennel fronds.
