Prepare the sauce. Combine dijon mustard, honey, garlic, lemon juice, olive oil, red pepper flakes, paprika, cayenne pepper, and salt and pepper.
Slice onion and lemon. Place vegetables on tin foil. Add salmon and top with prepared sauce.
Wrap the tin foil on the sides to create a pouch. Bake for about 15 minutes (depending on the thickness of the fish). Check after 15 minutes. If it’s still uncooked, place back in the oven for a couple of minutes.
Eat as is or enjoy with brown rice, quinoa, or salad.