In blender, combine broth and chilies; cover and process until pureed. Set aside. In a large skillet, saute onions in butter until tender. Stir in the chili powder, cumin, garlic and pureed mixture. Bring to a boil. Reduce heat to low; simmer, uncovered, for 20 minutes, stirring occasionally.
Add the brown sugar, orange juice, ketchup, and lemon juice. Cook and stir over low heat for 15 minutes or until thickened; keep warm.
For nuggets, combine the cornmeal, chili powder, cumin and salt in a large resealable plastic bag. Add chicken cubes, a few at a time, and shake to coat.
Heat oil in a large skillet; cook chicken for 6-8 minutes of until juices run clear, turning frequently. Serve with sauce.