Pesto Pasta Salad

Name: Pesto Pasta Salad
Ingredients: 1/2 medium lemon; 5 ounces baby spinach (about 5 cups); 1/2 cup basil pesto; 1/4 cup mayonnaise; 1/2 teaspoon kosher salt, plus more for cooking pasta; 1/4 teaspoon freshly ground black pepper; 1 pound dried short pasta, such as fusilli, rotini, or cavatappi; 1/2 medium English cucumber; 1 pint cherry or grape tomatoes (10 ounces); 8 ounces mini mozzarella cheese balls; Torn fresh basil leaves, for serving