For the White Chicken Chili, heat oil in large saucepan on medium-low heat. Add onion; cook and stir 5 minutes or until softened. Add remaining ingredients. Bring to boil on medium-high heat. Reduce heat to medium-low; simmer 15 minutes or until chicken is cooked through.
Meanwhile, for the Masa Dumplings, mix masa harina, oregano, sea salt and baking powder in medium bowl. Add egg and water; stir to form a dough. Shape dough into 1/4-inch balls. Use your pointer finger to make an indentation in center of each ball. Set aside.
Drop the Masa Dumplings onto chili after chicken is cooked through. Cover. Simmer 20 minutes or until dumplings are cooked through and liquid has reduced by a quarter. Serve chili with shredded cheese, chopped fresh cilantro, sliced jalapeño peppers and lime wedges, if desired.