Step 1

Preheat oven to 450°F. Line a large baking dish or a baking sheet with parchment paper and top with a rack.

Step 2

In a small bowl, mix together olive oil, lemon zest, chopped thyme, garlic, chile flakes and kosher salt.

Step 3

Cut 3 diagonal slashes down to the bone on each side of the fish. Season fish all over, including inside the slashes and cavity, with mixture.

Step 4

Lay on the rack and stuff each slash and cavity with the thyme stems, sliced lemons and kumquats.

Step 5

Cook, without turning, until fish flakes with a fork and flesh is opaque in the center, about 20 minutes.

Step 6

Carve fish into four portions and transfer to plates. Drizzle with juices from the baking dish and garnish with flaky salt before serving.