Heat oil in a medium saucepan over medium heat. Add onion and capsicum. Cook, stirring, for 3 to 4 minutes or until vegetables are softened. Add curry paste. Cook, stirring, for 1 minute or until aromatic.
Add stock and coconut milk. Bring to the boil. Add beans. Reduce heat to medium-low. Cook, stirring, for 4 to 5 minutes or until heated through.
Stir in spinach. Cook for 1 minute or until spinach is just wilted.