In a large skillet cook bacon over medium heat until crisp, turning once. Drain bacon on paper towels; crumble. Reserve bacon drippings in skillet.
Cook onion in reserved bacon drippings for 5 to 8 minutes or until onion is tender and golden brown. Set aside.
In a large saucepan cook macaroni according to package directions. Drain and return to saucepan. Stir in the crumbled bacon, onions, 1-1/2 cups of the mozzarella cheese, the gruyere cheese, half-and half, and pepper. Toss gently to combine. Spoon into a 1-1/2-quart casserole.
Bake, uncovered, in a 350 degree F ovenfor 20 minutes. Stir gently. Top with the remaining mozzarella cheese. Bake for 10 minutes more or until top of casserole is brown and bubbly. Let stand 10 minutes.