Meanwhile, cook and stir onions and garlic in grill pan or skillet on medium-high heat 5 min. or until crisp-tender. Remove from pan; peel garlic. About 30 min. before meat is done, blend remaining broth, tomato sauce, ancho peppers, chipotle pepper, 1/2 cup nuts, onions and garlic in blender until smooth. Heat remaining oil in medium saucepan on medium heat. Add prepared sauce; cook 15 min., stirring occasionally.