Bring a pot of water to a boil for the pasta and heat a cast-iron skillet or large griddle pan over medium-high heat.
Combine meat with Worcestershire, grated onion, salt and pepper, and form patties, 4 large or 8 small. Drizzle patties lightly with oil. Separate buns and arrange bottoms on a platter.
Undercook the macaroni by a minute in boiling salted water. Meanwhile, melt butter in a small pan over medium heat. Add garlic and chilies, and stir 3 minutes. Add pimientos and heat through. Add paprika then flour and stir 1 minute. Whisk in milk and let thicken. Season with salt and pepper then stir in cheese to melt. Add macaroni and stir to combine.
Cook burgers 3-4 minutes on each side for large burgers, 2-3 minutes on each side for sliders for medium doneness.
If using fixins, place them on bun bottoms. Place patties on bun bottoms and top with mac 'n cheese and set bun tops in place.