Place the pumpkin, evaporated milk, peanut butter, chopped green onions, garlic, cilantro, lime juice, soy sauce, sugar, and cayenne pepper in a blender or food processor; cover. Blend until smooth.
In a medium bowl, combine ½ cup of the pumpkin mixture with the chicken; cover. Reserve the remaining pumpkin mixture. Marinate the chicken in the refrigerator, stirring occasionally, for 1 hour.
Take chicken pieces out of their marinade, and alternately thread the chicken, bell peppers, and green onion pieces onto skewers.
Preheat the grill or broiler. Grill or broil, turning once, for 10 minutes or until the chicken is no longer pink. Heat the remaining pumpkin mixture; serve with satay for dipping.