Take neck and giblets and boil in 5 cups of water and salt and pepper for basting throughout roasting process. Bast every hour or so once it starts to get golden.
Rinse and dry the turkey. Preheat the oven to 400 degrees F. Season the turkey inside and out with salt and pepper. Prepare the peppers by arranging them under a low broiler until blackened. Put them in a large bowl and cover with foil until cool enough to handle. Remove the skin, stems and seeds (do not rinse under water) and dice.
In a medium saute pan over medium-high heat, add the canola oil and when hot, add the diced peppers and saute for 2 to 3 minutes. Add the, garlic, cumin, chopped cilantro and the scallions. Cook for 2 to 3 minutes and season with a little salt and pepper, to taste. Stir in the zest and juice of 1 lime, and deglaze with 1/4 cup of the tequila. Remove from heat, transfer to a plate, spreading evenly, and allow to cool.
Carefully run your hand under breast skin of the turkey, creating a pocket from the neck to the bottom of breast on both sides. Gently stuff half of the pepper mixture into each skin pocket, lay the bird on its back and even out the pepper stuffing. Trim any extra fat off the body and tuck the wings behind.
Put the onion, a 1/2 bunch of cilantro and the cut lime halves into the cavity and arrange on a roasting rack in a roasting pan.
Roast until the internal temperature registers 165 degrees F on an instant-read thermometer, about 15 to 20 minutes per pound, about 3 1/2 hours. Remove the turkey from the oven to a cutting board. Tent with aluminum foil and let rest for 15 minutes.
While the turkey is resting, skim any fat off the top of the pan drippings and heat over medium-high heat. Scrape any bits off the bottom and add the chicken stock. Reduce for 8 minutes, then lower the heat and add the half-and-half and remaining tequila. Reduce for 5 minutes and adjust seasoning with salt and pepper, to taste. Strain and hold warm.
Carve the turkey, arrange on a serving platter and serve with the au jus.