Cook the Pasta:

1. Cook spaghetti in a pot of very salty water until al dente. (I recommend prepping the rest of the recipe while you wait for the pasta to cook!)
2. When pasta is al dente, reserve 1/2 cup of the pasta water.
3. Drain pasta and set aside.

Sear the Barramundi:

1. Pat barramundi fillets with a paper towel to remove any excess moisture (this prevents sticking and helps the fish brown when you cook it!)
2. Lightly season both sides of the fish with salt. You can also add a bit of pepper here if you like!
3. In a large nonstick or cast iron skillet, heat oil over medium-high heat. Tip: To prevent sticking, make sure your pan (and your oil) are very hot before adding the fish. 
4. When the skillet is hot, carefully place barramundi in the pan. You should hear a nice sizzle!
5. Cook barramundi for about 2 minutes until the edges have begun to turn bright white. Carefully flip with a thin spatula and cook for two minutes more or until cooked through. Tip: If the fish is sticking to the pan, it needs to cook a little longer!
6. Remove cooked barramundi to a plate. Return the skillet to the burner over LOW heat - the pan is still hot, and you don't want to burn anything while you finish the sauce!

Make the Sauce:

1. Add butter to hot skillet and let it melt. Add garlic and red pepper flakes. Cook, stirring frequently, for a minute or two until the garlic is soft and fragrant. Tip: The skillet will be VERY hot here - keep a close eye on it so your garlic doesn't burn, and turn off the heat if you need to!
2. Stir lemon juice, lemon zest, and chopped parsley into the sauce. Bring it to a simmer, then use a ladle to remove a few Tablespoons of sauce and set it aside (you'll drizzle this over the top of the fish later!)
3. Add cooked pasta to sauce and toss to combine. Add reserved pasta water a Tablespoon at a time (you likely won't need it all) and toss well until pasta is evenly coated in the sauce. Taste and add salt and pepper as needed. 

Serve:

1. Top spaghetti with cooked barramundi pieces. Drizzle the reserved lemon sauce over the top, add extra parsley for garnish (optional) and serve immediately.