Cook pasta according to the package directions; drain. Return pasta to a hot pan, cover to keep warm. Set aside.
Meanwhile, in a large skillet, cook bacon over medium heat until crisp, turning once. Drain bacon on paper towels, reserving 3 Tbsp. bacon drippings in pan. Crumble and set aside.
Cook onion and garlic in the bacon drippings over medium heat for about 30 seconds. Stir in the flour, dry mustard and pepper. Add milk all at once. Cook and stir until thickened and bubbly; reduce heat. Add Gouda and cream cheese; cook and stir until almost melted.
Pour cheese sauce over the cooked pasta. Stir in oregano and all but 2 Tbsp. of the crumbled bacon. Transfer mixture to an ungreased 2-qt. rectangular baking dish; cover with foil. Bake in a preheated 350-degree oven for 25 minutes.
While dish is baking, melt butter in a new large skillet. Stir in brown sugar; add pear slices. Cook, turning occasionally, until pears are tender, about 6 to 8 minutes. Remove from heat. Remove foil from the baking dish. Stir about half of the cooked, sliced pears into the macaroni and cheese. Spoon the remaining pear slices atop macaroni and cheese; sprinkle with Parmesan and reserved crumbled bacon. Return to oven and bake 5 minutes more or until Parmesan has softened. Let stand for 10 minutes before serving.