In a food processor, pulse together the basil, garlic, pine nuts, lemon juice and zest. Add the Pecorino and half of the olive oil; pulse to form a thick paste. With the motor running, add the remaining olive oil in a steady stream. If you want a thinner pesto, feel free to add in another tablespoon of olive oil. Season to taste with salt and pepper.
Bring a large pot of water to boil, adding a generous amount of salt, and prepare a bowl of ice water. Add the haricots verts and cook until bright green and still slightly crisp, about 3 minutes. Quickly remove the beans with tongs and plunge into the ice water to cool. Drain and set aside.
Bring the water back to a boil and add the pasta. Cook per the package directions until al dente. Drain the pasta, reserving 1 cup of the pasta water.
Add the pasta back into the pot, along with the pesto, haricots verts, tomatoes, and ½ cup of pasta water, stirring to combine. Divide the pasta into serving bowls, and garnish with freshly grated Pecorino and freshly grated lemon zest.
*Last night I forgot to put the garlic in the pesto, and it was still really great! So feel free to eliminate if you would rather have a cleaner taste.
**If you can’t find haricots verts, you can use regular green beans. You just may have to blanch them slightly longer.