First, you’re going to need to segment that citrus. Using a sharp knife, carefully slice the top and bottom from the grapefruit. Remove the peel and white pith from all around the grapefruit. (Don’t worry if it’s not perfect people.)
Working over a medium bowl, cut between the membranes to release the grapefruit segments into the bowl. Repeat the peeling and segmenting process with the orange. Remove grapefruit and orange segments from the bowl and slice them crosswise into ½-inch pieces. Return the citrus to the bowl and add the lime juice, red onion, jalapeño, cilantro and a pinch of salt. Gently stir to combine. Refrigerate until ready to use.
Gently pat the halibut filets dry with paper towels. Season both sides of each filet generously with salt and pepper.
Heat the olive oil in a large skillet or sauté pan over medium-high heat. When hot, add the filets and cook for 3-4 minutes until golden brown on one side. Turn the filets and cook for another 3 minutes until opaque.
Place halibut on a serving platter or plates and top with citrus-jalapeño salsa.