Prepare the blood orange vinaigrette.

Reduce blood orange juice in a pan over high heat by half, then cool.

Combine reduced orange juice, Dijon mustard, red wine vinegar, and salt in a bowl.

Whisk to emulsify, gradually adding olive oil.

Set the vinaigrette aside.

Zest an orange and reserve the zest.

Segment the orange over a bowl, saving both segments and juices.

Sauté scallions in olive oil until softened.

Add mushrooms, salt, and pepper; sauté until softened.

Add radicchio, orange segments, and juice to the mushroom mixture.

Toss until radicchio wilts, then transfer to a platter to keep warm.

Combine orange zest, pine nuts, and fennel in a small bowl.

Heat olive oil in a pan until smoking.

Season tuna steaks with salt and pepper and sear to desired doneness.

Place tuna steaks on top of the radicchio mixture on the platter.

Drizzle with blood orange vinaigrette and top with the orange zest mixture.

Serve immediately.