My sister Maria's birthday is in March. This dish might be her birthday meal.
Bring a large pot of water to a boil for the pasta.
Preheat the broiler to high.
In a large skillet, heat the oil, two turns of the pan, over medium to medium-high. Add the garlic and stir until aromatic, about 1 minute. Add the artichokes, thyme, and lemon zest; season with salt and pepper. Cook, stirring occasionally, until lightly browned, 3 to 4 minutes. Add the cream. Cook over medium heat, stirring occasionally, until slightly reduced, about 10 minutes. Transfer to a food processor or high-power blender. Add the ricotta and Parm. Process until smooth. Return the sauce to the pan and keep warm over low heat.
In a small skillet, heat the chicken in the stock until heated through, 3 to 5 minutes.
On a broiler pan or baking sheet, arrange the radicchio in a single layer. Spray with cooking spray and season. Broil until slightly wilted and charred at the edges, 5 to 6 minutes. Coarsely chop the radicchio.
Meanwhile, salt the boiling water and add the pasta. Cook until al dente. Reserve about 1/2 cup of the starchy cooking water. Drain the pasta.
Stir the lemon juice into the sauce. Add the pasta and toss. Add the pasta cooking water if the sauce is too thick. Season the pasta and toss until coated.
Divide the pasta among shallow bowls. Top with the chicken and radicchio.