Heat the grill or grill pan to about 350°F.
Drizzle olive oil (or butter) onto 2 sheets of heavy duty foil. Place haddock directly on the greased foil.
In a small bowl, mix the orange zest, thyme, 1 tsp salt, and a pinch of cracked black pepper. Rub the mixture all over the haddock fillets.
Carefully seal the foil into packets and place them on the grill.
Grill the haddock in the foil packets for 8-10 minutes depending on the thickness of the filets. The fish should be opaque white and easily flake with a fork when it's done.
Carefully remove the foil packets from the grill and plate the haddock filets, pouring any juices over top.
Top with salsa just before serving.