Get out a saucepan that is plenty big enough to handle the shrimp and the tortellini. Put the shrimp (no need to defrost) and the tortellini in the saucepan and add enough water to cover it all by an inch or two. On the stove it goes with the burner set at high. When it comes to a rolling boil let it go on for just a minute. It is ready. Strain it and put it all back in the saucepan. Add the Pesto and gently mix until everything is covered with the pesto. If you want to, garnish it with some freshly grated parmesan and/or some dried basil.