In a medium sized bowl, whisk together the Dijon mustard, lemon zest, 1 tbsp of the lemon juice, 1 tbsp of the olive oil and half the minced garlic.
Add the salmon fillets and toss to coat in the mixture. Cover and leave to marinade for around 30 minutes but no longer than 1 hour.
Preheat the oven to 400°F (200°C). On a large baking tray, toss the courgette (zucchini) and cherry tomatoes with the remaining olive oil, garlic, oregano, salt, and pepper. Spread out the vegetables in one layer and roast in the oven for 12 minutes.
Remove from the oven and push the vegetables to the sides of the baking tray, creating space for the salmon. Place the salmon fillets in the centre of the tray. Bake the vegetables and salmon for 10-12 minutes, or until the salmon is cooked through and the vegetables are tender.
Remove the tray from the oven and drizzle the remaining 1tbsp of lemon juice over the entire dish.
Serve hot, with the roasted vegetables alongside the salmon and garnished with chopped parsley if desired.