Heat oil in large non-stick skillet over medium heat. Add onion; cook, stirring about 3 minutes. Add potatoes; cook until tender and golden, about 8 minutes. Season with salt. Whisk eggs in large bowl. Stir in onion/potato mixture, sweet pepper and parsley, if using. Pour egg mixture into skillet over medium heat; cook 1 minute. Reduce heat to low; cook until eggs are set in centre and lightly browned on bottom. Slide omelette onto large flat plate. Place another plate on top; flip to invert. Slide back into skillet; cook 2 to 3 minutes longer.