Preheat your oven to 400°F.
In a small bowl, mix together the softened butter, chopped cilantro, lime zest, sliced garlic, salt, pepper, and chili flakes (if using) to create a garlic butter paste.
Cut two large pieces of parchment paper, enough to fold over and fully enclose each salmon fillet in a sealed packet.
Place each salmon portion in the center of a parchment sheet.
Divide the garlic butter mixture between the two fillets, spreading it evenly over the top.
Squeeze the lime juice over each piece.
Fold the parchment over each fillet and tightly crimp the edges to seal the packets completely.
Place the parchment packets on a baking sheet and bake for 10 minutes.
After 10 minutes, turn off the oven and let the salmon sit inside for an additional 5–10 minutes depending on the thickness of the fillets.
Carefully remove the packets from the oven, open them, and serve the salmon hot with rice and/or vegetables.