Prep/clean your seafood, lightly salt each side of the shrimp and scallops, and keep chilled over ice or in the fridge until it's time to cook them.
Heat olive oil in a large braiser or skillet over moderate heat. Add the garlic and onion to the skillet and cook, stirring often, until garlic is fragrant and onions have become translucent; approx. 3-4 minutes. Careful not to brown the garlic.
Add DeLallo's Arrabbiata sauce to the braiser/skillet, along with TWO (2) cups of vegetable broth and linguini. Season with S+P, to taste. (Save the extra cup of broth.)
Bring the liquid to a boil, then reduce the heat and simmer, stirring occasionally, until pasta is cooked through. This should take approx. 18-20 minutes.
Stir in the scallops, shrimp, and mussels; ensure the seafood is covered with sauce and noodles to get an even cook. Add some extra vegetable broth, cover and allow to simmer for 4-6 minutes or until mussels have opened and the shrimp and scallops are opaque. Add additional broth if need be. Keep an eye on the shellfish so they don't overcook; if they overcook, they will become rubbery. (*See recipe notes)
Serve immediately, and garnish with some freshly grated Pecorino Romano, chopped fresh parsley, and a hunk of fresh Italian bread. You can sprinkle your serving with some red chili flakes if you *really* want to spice things up.