HEAT oil in large saucepan over medium-high heat. Add onion; cook, stirring occasionally, for 3 to 4 minutes or until tender. Add 4 cups corn; cook, stirring occasionally, for 4 to 5 minutes or until tender. Add water and bouillon; cook, stirring frequently, for 15 minutes or until corn is very soft.
PLACE corn mixture in blender or food processor; blend until smooth. Return to saucepan. Stir in remaining corn, evaporated milk, bell pepper and rosemary. Cook, stirring frequently, for 5 to 10 minutes or until chowder is thick and bell pepper is tender. Season with salt and ground black pepper, if desired. Garnish with basil.