Heat the oven to 350°F. Grease a ring mold. Pour béchamel sauce in a large bowl.
Melt the butter in a large saucepan, add onion and cook on a low heat for 3-4 minutes; add peas and stir to combine. Cover with broth and after 5-6 minutes add ham. Cook for 3 more minutes stirring frequently and set aside.
In the meantime, cook the Tortellini according to package instructions, drain and transfer to the saucepan; season with half Parmigiano Reggiano and toss to combine. Pour Tortellini in the béchamel bowl and stir gently. Then transfer to the greased mold.
Bake for 20 minutes. Let rest 10 minutes out of the oven. Unmold the Tortellini ring and serve with remaining Parmigiano Reggiano cheese.