Place pizza stone in oven. Preheat oven to 450°F. (Do not remove pizza stone while oven preheats.) Place pizza dough on a lightly floured surface, and cover with plastic wrap. Let stand 20 minutes.
Place 1 cup of the parsley in a small bowl. Stir in olive oil and garlic. Set aside.
Roll pizza dough into 10-inch round on a pizza peel or bottom of a sheet pan. Spread parsley mixture in an even layer on pizza dough, leaving a 1-inch border around edge. (There should be a light, even coating over entire pizza.)
Spread chopped clams in an even layer on parsley mixture. Sprinkle with crushed red pepper. Top with grated pecorino Romano. Carefully slide pizza onto hot pizza stone.
Bake in preheated oven until crust is golden brown and cheese is bubbly and melted, about 20 minutes.
Remove pizza from oven, and sprinkle with Parmesan cheese and remaining 1 tablespoon parsley. Squeeze fresh lemon juice from lemon wedge over pizza. Serve immediately.