In a large skillet over low heat toast pumpkin seeds, cumin seeds and oregano until fragrant and pumpkin seeds begin to pop, 6 to 7 minutes. Reserve 2 tablespoons toasted seeds, and transfer the remaining seeds to a blender or spice grinder and process until finely ground. Set aside.
In the bowl of a food processor combine onion, cilantro, jalapenos, garlic, lettuce, tomatillos and radish tops and puree until smooth.
In a large skillet or Dutch oven, brown chicken on all sides in vegetable oil over medium high heat, about 10 minutes, turning the pieces as they cook. Transfer chicken to a platter. Add the pureed vegetables to the hot skillet and cook for 3 to 4 minutes. Stir in chicken stock and ground seeds, and bring to a boil. Reduce heat to a simmer and cook until thickened, 10 to 15 minutes. Season to taste with salt and pepper, and add the cinnamon, if desired. Add the chicken pieces to the pan and return to a boil. Reduce the heat to a simmer, and cook, partially covered, until the chicken is cooked through and tender, about 40 minutes.
Serve over white rice with sliced radishes and reserved toasted pumpkin seeds.
Yield: 4 to 6 servings