For easier shucking, steam clams over simmering water for two minutes or just until their shells barely open. Run a knife or small screwdriver around a shell's edge, and pop it open. If you partially steam the clams, reduce the broiling time by a minute or two. The clams may be unsteady on the jelly-roll pan, so you can line the pan with a bed of rock salt for more stability.
Heat a medium skillet over medium heat. Coat pan with cooking spray. Add pancetta to pan; cook 6 minutes or until pancetta begins to brown, stirring occasionally. Add wine; cook until liquid evaporates (about 30 seconds), scraping pan to loosen browned bits. Add bell pepper, shallots, and garlic to pan; cook 4 minutes or until tender. Place pancetta mixture in a medium bowl.
Place bread in a food processor; pulse 10 times or until coarse crumbs measure about 3/4 cup. Add breadcrumbs, cheese, parsley, and black pepper to pancetta mixture; stir until blended.
Discard any clams with broken or open shells. Shuck clams; discard top halves of shells. Top each clam with about 1 rounded teaspoon pancetta mixture. Broil 4 minutes; turn pan. Broil an additional 3 minutes or until tops are browned and clams are done. Serve with lemon wedges, if desired.