Preheat the oven to 425° F (218° C)
Line a large sheet pan with aluminum foil.
Pat the filets dry and add salt and pepper to taste.
Zest the lemon.
Cut the lemon into 8 slices.
Separate the broccoli florets from the stalk, and discard the stalk. Cut any large florets into bite-sized pieces.
Separate the rosemary leaves from the stems, and discard the stems.
In a medium-sized bowl, combine the potatoes, 1/2 the lemon zest, oil, salt, and pepper. Once combined, place potatoes on the sheet pan.
In the same bowl, combine the broccoli florets, oil, remaining zest, salt, and pepper. Set aside.
Roast the potatoes for 30 minutes at 425° F.
Add the seasoned broccoli florets and fish filets to the sheet pan. Top the filets with the lemon slices and rosemary.
Divide the baked fish, potatoes, and broccoli onto 4 plates and serve!