Cook the spaghetti al dente according to the instructions on the packet.
Steam the pears in the vegetable stock and white wine for about 10 minutes. Drain and set aside the liquid.
Now heat the oil and butter in a saucepan until the butter melts. Then sweat the red onion and garlic in it for about 2 - 3 minutes. Then stir in walnuts, oregano and lemon juice. Now stir in the pears with 4 tablespoons of the cooking liquid. Crumble the blue cheese into it and let it melt for approx. 1 - 2 minutes over low heat while stirring. Salt and pepper.
Mix the sauce with the spaghetti, arrange on plates and serve.