Heat a large saucepan over medium-high heat. Place salmon filets flesh-side down on the pan and sear, 3-4 minutes. Flip filets to skin-side down and sear 1 minute.
Add a tablespoon of water to the hot pan, cover, and then turn the heat down to low. Let salmon steam 10-15 minutes, depending on thickness of the filets. Once salmon flakes easily with a fork, it’s done.
While the salmon is cooking, make the guac. Split the avocados, throw away the pits, and scoop the green flesh into a medium bowl. Squeeze in the juice of one lime. Use a potato masher to mash the avocado and juice together.
Add the red onion, cilantro, garlic powder, 1/2 tsp salt, and 1/2 tsp pepper. Mash a little more, and once the mixture is relatively smooth, you can stir it with a spatula to make sure all the ingredients are combined. Taste and season additionally if necessary. (**See Notes below)
Spoon a generous helping of guacamole over each piece of salmon. Serve immediately.