Put 1-inch of water in a 5-quart wide heavy pot, then put a steamer basket inside pot and bring water to a boil. Add broccoli and steam, covered, until just tender, 8 to 10 minutes.
Meanwhile, cook garlic in oil in a 12-inch heavy skillet over moderately low heat, stirring occasionally, until pale golden, about 5 minutes. Stir in panko, pepper, and salt, then increase heat to moderate and cook, stirring occasionally, until crumbs are golden, about 3 minutes.
Remove form heat, stir in zest. Transfer broccoli with tongs to crumb mixture in skillet and toss to coat.
Notes
Panko breadcrumbs can be found in your market's Asian food section.