Boil the pasta in salted water according to packet instructions, reserving 200ml of cooking water before draining.
Meanwhile, heat the olive oil in a large frying pan over medium heat. Add the diced onion and cook for 5 minutes until soft.
Add the minced garlic and oregano, cooking for 1 minute until fragrant.
Add the butter beans and gently mash about half of them with the back of a spoon. This creates a creamy texture without any cream.
Pour in 150ml of the reserved pasta water and stir well. The starch in the water combined with the mashed beans creates a silky sauce.
Add the drained pasta to the pan and toss everything together. Add more pasta water if the sauce seems too thick.
Stir in the grated cheese and parsley. Season with salt and pepper and serve immediately.