Pat the kingfish fillet completely dry with paper towels to ensure a golden crust.
Season both sides of the fish evenly with sea salt, black pepper, and garlic powder.
Heat the avocado oil in a large cast-iron or stainless steel skillet over medium-high heat until shimmering.
Carefully place the fish in the skillet, skin-side down, and press lightly with a spatula for 30 seconds.
Sear the fish undisturbed for 4-5 minutes until the skin is golden and releases easily from the pan.
Flip the fillet and add the asparagus spears to the empty spaces in the skillet.
Cook for another 3-4 minutes, tossing the asparagus occasionally, until the fish is opaque and the asparagus is tender-crisp.
Remove from heat, squeeze the fresh lemon over the fish and vegetables, and garnish with chopped parsley before serving.