Preheat the oven to 425˚F regular or 400˚F convection (see headnote).
On a rimmed baking sheet, toss the potatoes with 1 tablespoon of the olive oil and 1 teaspoon of oregano. Scatter the smashed garlic and lemon wedges around the potatoes and roast for 25 minutes.
1 lb potato, ¼ cup olive oil, 3 tsp oregano, 4 cloves garlic, 1 lemon
In the meantime, mix together the remaining olive oil (3 tablespoons), finely chopped garlic, kosher salt and pepper. On your work surface (I line it with parchment paper), season the fish with half of this mixture. Then use the remaining mixture to toss with the broccolini and tomatoes.
2 cloves garlic, 1/2 tsp salt, 1/8 tsp pepper, 24 oz cod, 1 bunch broccolini, 1 cup cherry tomato
After the 25 minutes, remove the potatoes from the oven and nestle the fish in and around them. Scatter and nestle the broccolini and tomatoes around the fish and potatoes. Then place the feta in the empty spots.
2 tbsp feta cheese
Return the pan to the oven and bake for 12-20 minutes or until the fish is cooked; it should flake when pierced with a fork.