Boil, steam or microwave potatoes until just tender; drain.
Meanwhile, heat 2 teaspoons of the oil in a medium saucepan over medium heat; cook onion and curry paste, stirring, for 3 minutes or until onion softens and paste is fragrant.
Stir in coconut milk and bring to a simmer. Add potato; cook for 5 minutes, stirring occasionally. If the sauce is a little thick add a couple of tablespoons of water. Press potatoes gently to crush slightly. Season to taste.
Heat remaining oil in a small frying pan over medium-high heat. Break egg into pan; fry egg until white is set and cooked to your liking.
Serve curry mixture on rice with fried egg, coriander, chilli and cucumber.
