Heat the olive oil in a large nonstick skillet set over medium heat. Add the onions and cook until softened, stirring occasionally, about 10 minutes. Cover and cook until the onions are golden brown, about 10 minutes, stirring occasionally. Season with salt and pepper.
Add ¼ cup water, cover the skillet again and cook until the onions are deep golden brown, about 20 minutes. You may need to add more water, 1 to 2 tablespoons at a time, throughout cooking to stop the onions from drying out. Each time you add water, use a wooden spoon to scrape up any brown bits and stir into the onions.
Stir in the garlic and red pepper flakes. Cook for 1 minute.
The salmon
While the onions are caramelizing, cook the salmon. First, lightly coat the salmon fillets with olive oil spray. Season with thyme, salt and pepper.
Either 1) bake in the oven (375 degrees F) until the salmon is cooked through, about 10 minutes OR 2) cook in an air fryer (370 degrees F) until the salmon is cooked through, about 7 minutes. Discard the skin and flake the salmon. Set aside.
The pasta
Bring a large saucepan of water to a boil. Season generously with kosher salt. Add the bucatini noodles and cook according to the package directions, until the pasta is al dente. One minute before the end of the cooking time, add the broccoli florets.
***IMPORTANT: Before draining the pasta, scoop out 1 cup of the pasta cooking water. This starchy water will be used to make the sauce.
Drain the pasta and broccoli into a colander. Transfer to the skillet with the caramelized onions. Toss the pasta with ½ cup of the reserved pasta water.
Add the Parmesan cheese to the pasta and toss again. Add the reserved flaked salmon, dill, parsley and lemon zest. Toss to combine with the remaining ½ cup of pasta water.
Taste and season with salt, pepper and additional dill and/or lemon zest, if desired. Serve.
Notes
Please note that I am not a medical or nutritional professional. I provide nutritional information for my recipes as a courtesy to my readers. It is calculated using the built-in recipe card calculator. While I attempt to provide information that is as accurate as possible, you should calculate the nutritional information independently before relying on it.