In a small bowl, mix together the lemon zest, lemon juice, olive oil, Dijon mustard, garlic, Creole seasoning, garlic powder, onion powder, salt, and pepper. Coat the salmon fillets with the marinade.
Preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper. Toss the asparagus and cherry tomatoes (if using) with 2 tsp of olive oil, salt, and pepper, then spread them evenly on the sheet. Make space in the center of the sheet for the salmon fillets. Place the salmon skin-side down on the sheet.
Place the sheet pan in the oven and bake for 10-12 minutes, or until the salmon flakes easily with a fork and the internal temperature reaches 122°F (50°C).
While the salmon is baking, melt the butter in a small saucepan over medium heat. Stir frequently for 4-6 minutes until the butter turns golden brown and begins to foam. Add the minced garlic, lemon juice, parsley, and dill (if using). Cook for 1 minute or until the garlic softens, then remove from heat to prevent the garlic from burning.
Drizzle the garlic brown butter over the salmon and asparagus. Serve the dish over mashed potatoes, if desired. Top with grated Parmesan, lemon wedges, and chopped parsley for extra flavor.