Heat the oil in a frying pan, add the mushrooms and cook over a high heat, stirring frequently, for 2 minutes until browned and softened.
Reduce the heat and add the garlic, thyme, soya or oat cream and soy sauce. Simmer, stirring, for 3 minutes, adding a little water if the sauce is too thick. Stir in the walnuts and season with pepper (the soy sauce is salty, so you won’t need to season with salt).
Spoon the mushroom mixture over the toasted bagels and garnish with thyme sprigs before serving.