Preheat oven to 190°C. In a small saucepan, melt the butter over low-medium heat. Add garlic and lemon juice and whisk until the mixture is well combined. Allow to cool down then add parsley, salt, pepper, and chilli flakes.
Cut out four squares of parchment, about 30cm long and wide. Place vegetable sticks in the center and add a piece of fish on top. Spread with the butter sauce. Sprinkle with a little salt, pepper, and additional chilli flakes if you want.
Fold parchment as follows: left side over the fish to the right, then the right side over to the left, so they overlap. Fold the top and bottom ends underneath to make a loose packet. Place the packets on a rimmed baking sheet and bake for 15 to 20 minutes, depending on your oven.
Carefully open the packets, transfer to plates drizzling the drippings on top and serve at once; or simply enjoy directly in the parchment packets!