Preheat the broiler. Remove papery outer layer from tomatillos then rinse them in warm water to remove some of their natural stickiness. Pat dry, then cut into quarters. Toss tomatillos and poblano with 2 teaspoons of the oil, place on a baking sheet and broil until charred, about 10 minutes.
Heat a large saute pan over medium heat. Add pumpkin seeds, peppercorns, allspice, and cumin and toast until pumpkin seeds are fragrant, 3 to 4 minutes. Transfer to a plate.
In same saute pan, heat 2 teaspoons oil over medium heat. Add onions and cook until soft and translucent, about 5 minutes, add the garlic and cook for 1 minute more.
Place tomatillos, poblano, onions and garlic, cilantro, chicken broth, jalapeno, toasted seeds and spices and salt in a blender and blend on high until totally smooth, about 30 seconds.
Heat the remaining 2 teaspoons olive oil in skillet and cook the chicken until browned on both sides and nearly cooked through, about 5 minutes per side. Add pepian sauce to skillet, covering chicken pieces. Bring to a simmer and cook an additional 3 to 5 minutes, until chicken is cooked through. Serve chicken topped with sauce and garnished with cilantro and lime wedges.