Preheat your oven to 390°F (200°C).
In a paella pan or large ovenproof skillet, heat olive oil over medium heat. Sauté the onion and bell pepper until softened, about 5 minutes.
Add the minced garlic and grated tomato, cooking for another 2 minutes.
Stir in the paprika, saffron, and season with salt and pepper. Cook for a minute to release the flavors.
Pour in the white wine and let it reduce by half.
Add the fideuà pasta and sauté for 2-3 minutes until it's well-coated in the sauce.
Pour in the fish stock and bring to a simmer. Let it cook for 5 minutes.
Carefully add the mixed seafood, distributing it evenly around the pan.
Transfer the pan to the oven and bake for 15-20 minutes, or until the seafood is cooked and the pasta is tender.
While the fideuà is in the oven, make the aioli. Crush the garlic with a pinch of salt using a mortar and pestle. Whisk in the egg yolk, then slowly drizzle in the olive oil while continuously stirring until the mixture emulsifies into a thick aioli. Stir in lemon juice and adjust the salt.
Remove the fideuà from the oven, let it sit for a few minutes, then sprinkle with chopped parsley.
Serve the seafood fideuà with a dollop of aioli on top or on the side.