Preheat oven: Set to 400°F (205°C) and line a sheet pan with parchment paper.
Prep the salmon: Rub salmon fillets with olive oil, lemon zest and juice, garlic, salt, and pepper.
Prep the vegetables: Toss zucchini, bell pepper, cherry tomatoes, and red onion with olive oil, oregano, salt, and pepper.
Arrange on sheet pan: Place salmon fillets in the center and surround with vegetables.
Roast: Bake 12–15 minutes until salmon flakes easily and vegetables are tender.
Cook grains (if using): Prepare quinoa or couscous according to package instructions while salmon roasts.
Assemble bowls: Divide grains into bowls, top with roasted vegetables and salmon, sprinkle parsley, and add optional toppings.