Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package directions, adding the broccolini during the final 3 minutes of cooking. Reserve 1/2 cup of pasta cooking water; and drain.
Return the pasta and broccolini to the cooking pot. Add the reserved cooking water, tomatoes, pesto, and salt. Serve with grated Parmesan cheese if using.
Blend spinach pesto in food processor: baby spinach, basil leaves, olive oil, walnuts, Parmesan cheese, salt, and garlic. Cover with olive oil. Store in the fridge for up to 5 days.
Wash and dry the Boston lettuce. Store in a paper towel-lined zip-top bag.