Rinse the turkey breast under cool water and pat dry. In a 1-gallon resealable plastic bag, add the beer, mustard, agave, salt and pepper. Stir well to combine, then add the turkey breast, making sure it is fully coated with the marinade. Put the bag into a bowl to avoid any leakage and refrigerate for 45 minutes. Do not marinate it longer than 45 minutes or the breast will become overly salty. While the turkey is brining, prepare the Red Bell Pepper Pesto.
Preheat an oven to 375 degrees F.
Drain the turkey brine and put the breast on a rack in a shallow roasting pan (Chef's Note: Do not rinse turkey). Roast until the internal temperature reaches 165 degrees F, on an instant-read thermometer, inserted in the thickest part of the breast, about 1 hour. Remove the turkey from the oven and allow it to cool. This entire process can be done ahead of time. Refrigerate the meat until you are ready to assemble the sandwich.
After the turkey has cooled, remove all of the meat from the bone and slice it diagonally into 1/2-inch thick portions. Roughly chop 3/4 cup of the giardiniera vegetables and add them to a small bowl. Add 4 tablespoons of the Red Bell Pepper Pesto and toss to combine. Slice the bread, and lightly spread the pieces with some of the leftover pesto. Begin layering your sandwich with the provolone on the bottom, then the sliced turkey and the giardiniera mixture. Top everything with the Rojo Rings, cover with another slice of bread and then serve.
Roasted Red Bell Pepper Pesto:
Set a grill to high heat. Grill the red bell peppers until the skins have blackened. Remove them from the heat and put them in a small bowl. Cover the bowl and let them steam. Cool them from 10 minutes to 1 hour, then carefully remove the skin and seeds. Do not rinse them with water.
Add the roasted peeled peppers, basil, garlic, cheese, nuts, red pepper flakes, anchovy paste, salt and pepper to a food processor. Pulse until fully combined. Gradually add in the olive oil while the processor is running and adjust seasonings, if necessary. Refrigerate the pesto until ready to use.
Rojo Onion Rings:
In a heavy bottom skillet or deep-fryer, heat the oil to 370 degrees F.
Combine the hot sauce, ketchup and water in a shallow bowl until incorporated. In 4 separate, shallow bowls or pie pans, separate the buttermilk, flour and panko and put all the bowls in this work order: buttermilk, flour, hot sauce mixture, panko bread crumbs.
Dip the onion rings into the buttermilk, then in the flour, then into the hot sauce mixture and finish them with the panko.
Submerge the rings in batches and deep-fry until bright red and starting to brown, about 2 to 3 minutes, turning as needed. Once fried, remove them from the oil to a plate lined with a paper towel and sprinkle with sea salt.