In 10-inch nonstick skillet, heat oil over medium heat. Cook onion, bell pepper and ham in oil 3 to 5 minutes, stirring occasionally, until vegetables are crisp-tender. Pour egg mixture into skillet. As eggs begin to set at bottom and side, gently lift cooked portions with spatula so that uncooked egg can flow to bottom. Cook 3 to 4 minutes or until eggs are thickened throughout but still moist; stir cheese into eggs.