Bring a large pot of water to boil and season generously with salt. Cook pasta according to package instructions.
Meanwhile, heat olive oil in a large pan over medium heat. Saute garlic and chilli flakes for 2 minutes until fragrant.
Add in onions, saute for 5 minutes until golden and softened.
Season with salt and black pepper. Then stir in tomato passata and add in mixed seafood. Simmer for 5-10 minutes until starting to thicken and the seafood cooked through. It might take a little bit longer if cooking the seafood directly from frozen.
Add in cooked pasta and fresh parsley. Toss to combine. Serve immediately.
Notes
If using frozen seafood, it's best to check the package instructions whether you could be cooking directly from frozen. I personally prefer to thaw beforehand if time allows.
Tomato Passata is pureed and strained tomato, which makes a great thick tomato sauce for the pasta. You could use tinned chopped tomatoes as well but it would take a little longer time for it to break down and cook into a sauce.