Roll out loaf into 12x16 rectangle. Cover with plastic wrap and let rest for 10-15 minutes. I roll it out on a piece of parchment paper to make transferring it easier.
Cook spaghetti according to directions for al dente. Drain and let cool slightly. Mix with sauce.
Remove wrap from dough. Place spaghetti lengthwise in a 4-in strip down the center of dough. Top with cheese cubes. You can add 1/2 lb. Italian Sausage or ground beef (cooked) on top of this if you want.
Make cuts 1 1/2 inches apart on long sides of dough within 1/2 inch of fillings.
Begin braid by folding top and bottom strips toward filling. Then braid strips left over right, right over left, etc. Finish by pulling last strip over and tucking under bread.
Transfer to sprayed baking sheet or I just leave it on the parchment paper and transfer to sheet. Brush with egg white. Sprinkle with parm, parsley, and garlic.
Bake at 350 for 30-35 min or until golden brown. Let cool slightly, slice and serve.