How to Make It
Marinate the chicken In a food processor, puree all of the ingredients except the chickens. Divide the marinade between 2 very large resealable plastic bags. Add a chicken to each and seal. Refrigerate for 24 hours.
Meanwhile, make the sauce In a food processor, puree the roasted bell pepper until smooth. Transfer to a heatproof medium bowl and stir in the onion, scallions, jalapeño, parsley, garlic, thyme and boiling water. Let cool, then stir in the lime juice and oil. Season generously with salt and pepper.
Light a charcoal grill. When the coals are glowing, rake them to one side and place a large foil pan on the other side for indirect cooking. Heat the grill to 375°.
Remove the chickens from the marinade, scraping off some excess; reserve the remaining marinade. Set the chickens skin side up in the foil pan on the grate. Close the grill and cook until well browned, about 20 minutes. Brush the chickens generously with the reserved marinade, close the grill and cook until the marinade starts to char in spots, about 20 minutes.
Turn the chickens skin side down and cook, uncovered, until charred and an instant-read thermometer inserted in the thigh registers 165°, 20 to 30 minutes; use a spray bottle filled with water to stop flare-ups. Transfer to a carving board and let rest for 10 minutes, then carve and serve with the sauce.