Chicken Under a Brick with Avocados and Chiles

Name: Chicken Under a Brick with Avocados and Chiles
Ingredients: 1 3 1/2–4-pound chicken, backbone removed; 1 tablespoon kosher salt plus more; 1 /2 teaspoon freshly ground black pepper plus more for seasoning; 1 /4 teaspoon cayenne pepper; 4 tablespoons olive oil, divided; 2 tablespoons finely grated lemon zest; 3 tablespoons fresh rosemary leaves; 1 large fresh poblano chile, quartered, seeded; 1 large red bell pepper, quartered, seeded; 1 red onion, cut into 1/2' slices; 1 /4 cup (or more) red wine vinegar; 2 garlic cloves, sliced; 1 cup fresh basil leaves; 4 avocados, halved and pitted; 1 /4 teaspoon chili powder