In a large skill, saute the onion until translucent, then add the pancetta. Cook until the onion is golden brown and the pancetta is cooked through. Add the peas and cook over medium heat for a couple of minutes, and then add the radicchio, cooking until wilted. Add salt and pepper.
Meanwhile, cook the pasta until 1 minute shy of al dente and drain, reserving 1 cup of the cooking liquid. Into the reserved cooking water, add the saffron and stir until bright yellow.
Add the pasta to the pea and radicchio mixture, and then mix in the saffron water. Stir until hot, and serve immediately with a sprinkle of parmesan.