Heat a large skillet over medium-high heat. Cook and stir beef in the hot skillet until browned and crumbly, 5 to 7 minutes; drain and discard grease.
Bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water, stirring occasionally until cooked through but firm to the bite, about 12 minutes. Drain.
Heat spaghetti sauce in a saucepan over medium heat; stir in ground beef and cook until sauce reaches a low simmer, about 5 minutes.
Place garlic bread on a baking sheet and cook in the preheated oven until golden brown, 15 to 25 minutes.
Spread spaghetti sauce onto the plain side of each piece of garlic bread; top with tomatoes and oregano. Mix remaining sauce with spaghetti and scoop spaghetti onto 1/2 of the bread slices. Place the bread slices without spaghetti on top of spaghetti layer, forming a sandwich. Pour any remaining sauce over sandwiches.