I always start by getting my oven ripping hot at 450°F (230°C). A high temperature is what gives the chicken skin that deep golden color and helps the vegetables caramelize instead of turning mushy. Don't skip preheating fully, or the pan won't roast evenly.
In a small bowl, I whisk together the olive oil, garlic, lemon juice, minced herbs, and chili flakes, then season with salt and pepper. I always set aside about 2 tablespoons of this mixture before touching the chicken. That reserved portion becomes the finishing glaze later.
I drop my chicken thighs into a large resealable bag, pour in the remaining herb mixture, and massage it evenly over every piece. This step only takes a minute, but it's where most of the flavor gets locked in. Set the bag aside while you prep the vegetables.
I scatter the sweet potatoes, Brussels sprouts, apples, and shallots across the sheet pan in a single layer. A light drizzle of olive oil plus salt and pepper goes over the top. Crowding the pan leads to steaming, so I always use my largest sheet pan for this harvest sheet pan chicken.
Next, I sprinkle the chopped bacon evenly over the vegetables, since it bastes everything as it renders. Then I nestle the marinated chicken thighs on top, spacing them out so the skin gets direct heat. This layering is the real secret to this one pan autumn chicken dinner.
I slide the pan into the oven and roast for about 30 minutes, checking that the chicken hits 165°F (75°C) on an instant-read thermometer. The vegetables should be fork-tender and slightly caramelized at the edges by this point.
For extra-crispy skin, I switch the oven to broil for 3 to 5 minutes, watching closely so nothing burns. This final blast of heat is what makes the chicken skin shatter instead of just being soft.
Right before serving, I brush that reserved 2 tablespoons of herb marinade over each chicken thigh. It adds one more layer of bright, garlicky flavor and makes the whole pan glisten beautifully.