Bring a saucepan of water to a boil. Cook 1 cup fideo according to package directions until al dente. Drain and toss with a light drizzle of olive oil.
Cook 4 ounces diced pancetta in a stainless steel skillet over medium heat until fat has rendered and pancetta is browned, 5–8 minutes.
Using a slotted spoon, transfer pancetta to a bowl. Reserve drippings in skillet.
Add 1 diced shallot to skillet and cook, over medium-low heat, until softened, about 5 minutes.
Add ¾ teaspoon fennel seeds and ¼ teaspoon red pepper flakes and cook 30 seconds. Deglaze with 2 tablespoons vermouth; simmer until nearly completely reduced and a ribbon formed on the pan fills in after 5 seconds, about 2 minutes.
Add clams, cover, and cook over medium heat until clams open, 8–10 minutes.
Heat oven to broil with rack set in lower-middle position (about 12 inches from element).
Pour clams and broth into a baking dish.
Toss cooked fideo with cooked pancetta and ½ cup breadcrumbs; pile over top of clams.
Broil until bread crumbs are browned and crispy, 12–15 minutes.
Meanwhile, combine ¼ cup mayonnaise, ½ teaspoon garlic and 1 teaspoon vermouth; season to taste with salt and pepper.
Remove dish from oven and dollop vermouth aioli over top. Sprinkle chopped parsley over top and serve.