Preheat oven to 425°F (220°C). Line a baking sheet with foil or parchment and lightly oil. Pat salmon dry and season with salt and pepper.
Melt butter gently and stir in minced garlic, lemon juice, lemon zest, Dijon (if using), parsley, and red pepper flakes. Taste and adjust seasoning.
Place fillets on the prepared sheet, spoon half the garlic butter over the tops, and bake for 10–12 minutes for 1-inch-thick fillets, or until salmon flakes easily.
Remove from oven, spoon remaining garlic butter over fillets, let rest 2–3 minutes, then serve with lemon wedges and fresh herbs.
Notes
For a crisp top, broil for the last 1–2 minutes, watching carefully to avoid burning.
Make the garlic butter up to two days ahead and gently warm before using.
Use an instant-read thermometer: 125–130°F (52–54°C) yields medium, tender salmon.