Pre-heat oven to 325°F.
Line a sheet pan with parchment paper.
Pat the salmon dry; place on the tray, skin-side down, if there is skin, and season with salt and pepper.
In a medium bowl, stir together the dill, ginger and olive oil until combined; season with salt and pepper.
Spread half of the dill-ginger mixture over the top of the salmon; reserve the remaining dill-ginger mixture.
Place in the pre-heated oven and bake until cooked through; 15 to 20 minutes; the salmon is done when the fish flakes or an instant-read thermometer inserted into the thickest part is 120°F.
As the salmon cooks, cut off the top and bottom of the grapefruit and set the grapefruit down on one of the cut sides.
Follow the curve of the fruit to cut away the peel and pith.
Squeeze the peels into the remaining dill-ginger mixture to get out any juice.
Cut the fruit in half, from top to bottom; slice into 1/4-inch-thick half-moons and remove the seeds; if pieces are especially large, halve them again.
Transfer the fruit and any juice on the cutting board to the bowl.
Repeat with the oranges.
Add the radishes, season generously with salt and stir gently to combine.
Peel and pit the avocado; quarter lengthwise; set aside.
Break the salmon into large pieces and divide across plates with the citrus salad; add the avocado to plates; season with salt.
Spoon the juices from the bowl over top and season with black pepper, another drizzle of olive oil and flaky sea salt, if using.
