Bring a large pot of water to a boil, salt it, add the spaghetti and cook until al dente. Drain, reserving 1 cup pasta cooking water.While the pasta is working, trim off the top of the fennel bulb and save 2 tbsp. of chopped fronds. Quarter, core and thinly slice the fennel. Thinly slice the celery on an angle.
In a salad bowl, dress the fennel, celery and parsley with the lemon juice, a good drizzle of EVOO, salt and pepper.
Meanwhile, in the pasta pot, heat 1/4 cup EVOO over medium heat with 2 tsp. pepper for spicy, or 1 tbsp. for very spicy. Stir in the reserved pasta water and the ricotta. Add the pasta, pecorino-romano and parmigiano-reggiano; toss. Top the pasta with the fennel fronds and serve the salad before or after.