Trim and halve the brussels sprouts. Using a vegetable peeler, peel thick strips of lemon zest, then coarsely chop. (You should have about 2 teaspoons chopped zest.)

In a large (preferably 12-inch) skillet, heat 3 tablespoons olive oil over medium-high. Add the brussels sprouts, season with 1/2 teaspoon salt and a few grinds of pepper, then arrange the brussels sprouts in an even layer, cut-side down. Scatter the lemon zest over the top and cook, undisturbed, until the brussels sprouts are well browned underneath, 3 to 5 minutes. Add the red-pepper flakes, stir and cook until the brussels sprouts are crisp-tender, 2 to 3 minutes. Transfer to a medium bowl.

In the same skillet, heat the remaining 1 tablespoon olive oil over medium-high. Break up any gnocchi that are stuck together, add them to the pan and cook, covered and undisturbed, until golden brown on one side, 2 to 4 minutes. Add the butter and honey, season with salt and a generous amount of black pepper, and cook, stirring, until the butter is golden, nutty smelling and foaming, 1 to 2 minutes. Stir in the brussels sprouts until warmed through. Serve with grated Parmesan.