01 -
Preheat the oven to 400°F for toasting the buns.
02 -
Heat a large skillet over medium-high heat, add butter, and cook the ground beef and onions until browned and softened, about 5–6 minutes. Drain excess grease.
03 -
Add water and spaghetti pieces to the skillet. Spread evenly, cover with a lid, and cook over medium-high heat for 4 minutes.
04 -
Uncover, stir in marinara sauce, salt, pepper, onion powder, and garlic powder. Stir to combine, then reduce heat to low.
05 -
Place buns cut-side up on a baking sheet, spread with garlic butter, and toast in the oven for 4–6 minutes until edges are golden.
06 -
Stir shredded mozzarella into the skillet until melted and the mixture becomes thick and cheesy.
07 -
Scoop generous portions of the cheesy spaghetti mixture onto toasted buns and serve immediately.