Whirl the bread in a food processor or blender to make bread crumbs. Melt the butter in a small skillet. Add the bread crumbs and sauté over medium heat until toasted.
Grate the zest from the lemon. Cut the lemon in half and squeeze the juice from one half into the pan. Add the salt and several grinds of black pepper and cook, stirring constantly, until dry. (The Lemon Crumbs can be made to this point up to 2 days ahead. Spoon into a plastic bag and set aside at room temperature.)
Microwave the broccoli according to the package directions. (If using fresh broccoli, pile the florets on a microwave-safe plate and sprinkle with a few tablespoons of water. Cover with plastic wrap and microwave 3 to 5 minutes or until crisp-tender.) Remove and sprinkle with the Lemon Crumbs.