Preheat oven to 400°F and line a baking sheet with parchment paper. In a bowl, season the sliced acorn squash with olive oil, kosher salt and cracked black pepper. Roast for about 8-10 minutes until the squash becomes fork tender.
In a small bowl, whisk together the apple cider vinegar, olive oil, Dijon, tarrago and maple syrup. Season with salt and black pepper.
In a medium bowl, add the radicchio, acorn squash and apple slices. Add the dressing and toss everything together.
To assemble the sandwich, add a generous amount of the chicken salad to one side of the focaccia and top it with the dressed radicchio, acorn squash, granny smith apples and pickled red onions. Enjoy!