1 large bulb fennel
Kosher salt, to taste
1 lb. fingerling potatoes, halved lengthwise
7 tbsp. extra-virgin olive oil
1 lb. fresh linguiça or kielbasa, cut into 1⁄4"-thick slices
1 whole cleaned red snapper (3 lbs.)
1 lemon, sliced into 1⁄4"-thick half moons
Ground black pepper, to taste
10 sprigs thyme, plus 2 tbsp. thyme leaves
10 sprigs parsley
1⁄2 lb. mixed olives, pitted
12 littleneck clams
1⁄2 cup white wine
Zest of 1 orange
Trim and discard stalks from fennel; reserve 10 wispy fronds. Halve fennel bulb lengthwise; slice into 1⁄4"-thick wedges. Bring 2 qts. salted water to a boil in a 4-qt. saucepan. Blanch fennel for 4 minutes; drain and set aside. Add potatoes to boiling water; reduce heat to medium; simmer until tender, 12–15 minutes. Drain potatoes; set aside.
Heat 2 tbsp. oil in a 12" skillet over medium-high heat. Add sausage; cook until browned, about 5 minutes. Set aside.
Heat oven to 475. Cut 4 angled slits on each side of fish, about halfway to bone. Put a lemon slice into each slit. Line a baking sheet with an 18" x 24" sheet of heavy-duty foil. Transfer fish to foil. Rub with 3 tbsp. oil; season with salt and pepper. Stuff cavity with remaining lemon, thyme sprigs, and parsley. Arrange fennel, potatoes, sausages, olives, and clams around fish; sprinkle with remaining thyme. Drizzle with wine. Put an 18" x 24" piece of foil over top. Crimp edges together to form a packet.
Roast for 35–40 minutes. Cut into foil; carefully pull back edges. Sprinkle with zest, remaining oil, and fennel fronds.