Start by seasoning the salmon fillets with salt and pepper.
Preheat your grill to medium heat.
While the grill heats, prepare the avocado sauce. Combine avocado, lemon juice, cilantro, garlic, salt, pepper, and olive oil in a blender.
Blend until smooth. If the sauce is too thick, add water to reach the desired consistency.
Place the salmon on the grill, skin-side down.
Grill for about 5 minutes on each side or until the salmon easily flakes with a fork.
Remove the salmon from the grill and let it rest for a couple of minutes.