Preheat your oven to 400°F (200°C). Line a large, rimmed baking sheet with parchment paper or a silicone baking mat. This not only prevents sticking but makes clean-up a total breeze.
In a small bowl or liquid measuring cup, whisk together 3 tablespoons of the olive oil, the minced garlic, lemon zest, lemon juice, dried oregano, smoked paprika, salt, and black pepper. This simple mixture is going to do a lot of heavy lifting for flavor.
Place the broccoli florets, bell pepper strips, and red onion wedges on one half of your prepared sheet pan. Drizzle with about half of the herbed oil mixture (save the rest). Use your hands or a spatula to toss the vegetables until they’re coated evenly.
In a separate bowl, whisk together the remaining 1 tablespoon of olive oil and the remaining herbs and lemon juice. Then, toss the fish fillets with this mixture and place them on the other half of the sheet pan, skin-side down if applicable.
Place both halves of the sheet pan directly into the oven and bake for 10 minutes. After 10 minutes, flip the fish fillets and vegetables and drizzle the remaining herbed oil mixture over them. Return to the oven for an additional 10 minutes or until the fish is opaque and flakes easily with a fork and the vegetables are perfectly blistered.
For the garnish, sprinkle fresh parsley and a squeeze of lemon juice over the sheet pan. Serve immediately.