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 to only cut away the peel and bitter pith
. Hold the fruit in one hand over a bowl and cut the flesh of the grapefruit away from the membrane to release a wedge. Repeat until all the segments are released.
In a large saute pan over medium heat, coat with olive oil and add the fennel. Season with salt and saute until the fennel is warm and coated with the oil, 1 to 2 minutes. Remove from the heat. Toss in the grapefruit segments, olive slivers, and juice and sprinkle with the fennel fronds. Serve immediately.