Pour lemon juice over the salmon fillets and gently rub to coat. Let sit for 10 minutes to allow flavors to infuse.
In a small bowl, whisk together mustard, honey, garlic, olive oil, salt, lemon juice, thyme, and lemon zest until smooth.
Preheat the oven to 200°C (390°F). Line a baking tray with parchment paper and place the salmon fillets on it.
Brush each fillet generously with the prepared sauce.
Optional: Toss asparagus and carrot sticks with olive oil, salt, and pepper, and arrange them around the salmon in the same tray.
Bake for 18–22 minutes, depending on the thickness of the fillets, until the salmon is cooked through but still moist and tender.
Before serving, sprinkle a little extra lemon zest on top for a fresh burst of flavor.