Set the oven to 350°F before beginning assembly. A fully heated oven helps the bread crisp while the cheese melts.
Cover a baking sheet with parchment to catch any escaping cheese. Keep the parchment flat so both bread halves sit steadily.
Split the French loaf lengthwise and scoop the soft center from both pieces with a spoon, leaving about a half-inch along the bottom and sides. Each shell should form a deep channel without holes or thin, floppy edges.
Arrange both bread shells cut-side up on the lined sheet. Leave enough space between them to keep their sides from pressing together.
Stir the garlic powder into the melted butter in a small bowl. The mixture should look evenly speckled rather than clumped.
Coat the exposed crumb inside both shells with the garlic butter. A light, even sheen across the bottom and walls signals good coverage.
Fold the browned beef and Italian seasoning into the tomato sauce in a medium bowl. The beef should remain evenly suspended in a thick, spoonable mixture.
Toss the Parmesan with the mozzarella in a separate small bowl. An even blend distributes the stretchy cheese and sharper flavor throughout the filling.
Fit one cooked lasagna noodle along the bottom of each bread boat. The pasta should lie comfortably inside the channel without pushing the bread walls outward.
Divide half the meat sauce between the two noodles, using ¼ of the full mixture for each boat. Spread it along the length so neither end has a heavy mound of filling.
Cover each sauce layer with ¼ of the cheese blend, then repeat the noodle, sauce, and cheese layers using everything remaining. Both boats should finish with cheese on top and evenly filled centers.
Bake for 15 to 20 minutes, then bring the bread to the table while hot. Look for melted cheese, bubbling edges, and a golden crust with a toasted garlic aroma.