Cook the tortellini in boiling water, as per pack instructions.
Meanwhile, melt the butter in a frying pan, add the walnuts and tomatoes and fry gently for 5 minutes until the walnuts are toasted and the tomatoes just softened.
Remove the tomatoes from the pan and set aside, then remove the walnuts. Add the spinach and stir lightly until it's wilted down.
Drain the tortellini and serve with the walnuts, tomatoes and spinach.