Step 1

Place a rack in middle of oven; preheat to 425°. Heat a large ovenproof skillet, preferably cast iron, over medium-high. Cook bell peppers in skillet, turning every minute or two, until blistered in several spots, about 5 minutes. (You aren’t trying to cook them, just get some color on them.) Transfer bell peppers to a cutting board and let cool slightly; reserve skillet. Stand a pepper upright and slice off sides, working your way around stem in 3 or 4 cuts. Pull out ribs and seeds; discard along with stems. Repeat with remaining peppers.

Step 2

Return peppers to skillet and add shallot, chile, and 3 thyme sprigs. Season generously with salt and black pepper and drizzle ¼ cup oil over. Season chicken all over with salt and black pepper and set on top of peppers. Place a lemon half and remaining2 thyme sprigs in chicken cavity and rub skin all over with remaining 1 Tbsp. oil. Roast in oven until skin is golden brown and crisp all over and an instant-read thermometer inserted into the thickest part of breast registers 160°, 60–80 minutes. Remove from oven (be careful; handle is hot!) and let rest 15 minutes before transferring chicken to a cutting board and carving.

Step 3

Just before serving, squeeze remaining lemon half over chicken and bell peppers.