Make the Spice Mix: Combine the oregano, fennel seeds, and red pepper flakes in a sealed container. This spice mix can be stored at room temperature for up to one month.
Prepare the Oven and Baking Racks: Adjust your oven racks to the lower third of the oven. Preheat the oven to 450°F, using the convection setting if available for even cooking.
Season the Broccoli: In a large bowl, toss the broccoli florets with olive oil, 1 tablespoon of the prepared spice mix, kosher salt, black pepper, and lemon zest. Mix well to ensure the broccoli is evenly coated.
Spread and Roast: Arrange the seasoned broccoli in a single layer on two baking sheets. Place them in the oven and roast for about 10 minutes.
Stir and Rotate: Remove the sheets from the oven and stir the broccoli to promote even caramelization. Swap the positions of the baking sheets to ensure both trays roast evenly.
Finish Roasting: Return the sheets to the oven and continue roasting for another 5 to 10 minutes, or until the broccoli is golden brown and tender.
Add Lemon Juice: Transfer the roasted broccoli to a serving dish and drizzle with 1 teaspoon of freshly squeezed lemon juice. Taste and add more lemon juice, if desired, for extra brightness.
Serve: Serve the broccoli immediately, either hot or at room temperature. This dish pairs well as a side or can be enjoyed on its own as a flavorful snack.