Add cubed bread to a large mixing bowl and set aside.
Melt butter over low heat and add minced onion. Sprinkle with salt and pepper. Stir to combine.
Drizzle melted butter mixture over cubed bread and stir to coat/combine.
Crumble ground turkey into a separate bowl and grate onion over the meat. Stir or 'smush' into the turkey.
Place a large sheet of wax paper on counter or tabletop. Dump meat mixture onto wax paper and flatten into a large rectangle (about 1/2 inch thickness).
Run a line of cubed/herbed bread down the center of the meat length-wise. Spread out and press down slightly to within 1 inch of the edges.
Starting with a short end, roll tightly sealing the seams and ends as you go. Seal completely and shape into a large loaf shape.
Place seam side down in a oiled/sprayed 9"x12" baking pan.
Bake in a 375 degree oven for 45 minutes or until the center temperature reaches 180 degrees on a meat thermometer.
Cool, in the pan, on a wire rack for 10 minutes before slicing.