How to Make It
Place oven rack on highest position and preheat broiler. Place tomatillos on a baking sheet and rub with 1 tsp. oil. Broil tomatillos, turning occasionally with tongs, until skin blisters, about 10 minutes. Allow to cool slightly. Chop and place in a large (6- to 7-quart) slow cooker.
Pat chicken dry and sprinkle with salt and pepper. Warm 2 Tbsp. oil in a large skillet over medium-high heat. Working in batches, brown chicken on all sides, about 5 minutes per batch. Transfer browned chicken to slow cooker.
Add 2 tsp. oil to skillet. Add onion, garlic, both peppers and cumin, season with salt and pepper and cook, stirring occasionally, until onions and peppers begin to soften, about 10 minutes. Add chicken broth, sugar and lime zest and cook for 2 minutes, stirring and scraping up any browned bits from bottom of pan. Pour mixture over chicken in slow cooker. Cover and cook on low until chicken is tender and vegetables are very soft, 6 to 7 hours. Season with more salt and pepper, if desired.
Preheat oven to 350°F. Line a baking sheet with parchment. Use a sharp paring knife or a cookie cutter to cut ghost shapes out of tortillas. Brush about 1 tsp. oil on both sides of tortillas and place on prepared baking sheet. Bake until crisp, about 15 minutes. Remove from oven, then sprinkle with salt. Serve chili with sour cream, scallions and tortilla ghosts.