Immerse the tomatoes in boiling water for a few seconds then rinse under cold water, peel and remove the seeds. Put the almonds, pine nuts, walnuts, peeled garlic clove and a piece of chili pepper in the mixer and blend until the mixture is uniform and finely ground.
Stop the motor and add the tomatoes, oil, mint leaves and salt. Blend again for half a minute and pour the pesto into a tureen. Cook the spaghetti al dente, drain and pour into the tureen. Mix well and serve immediately.
The cold sauce will inevitably cool off the pasta: if you want it to be warmer, while the pasta is cooking place the tureen on top of the pot for a few minutes.