Begin by preparing the brussels sprouts by trimming the outer leaves and then halving them. Using a vegetable peeler, (or carefully with a sharp knife) peel thick strips of lemon zest, then coarsely chop. (You should have about 2 teaspoons chopped zest.)
Then, heat 3 tablespoons olive oil over medium-high heat in a large skillet. Combine the brussels sprouts with 1/2 teaspoon salt and a few grinds of black pepper. Using a heat safe spoon, 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, about 3 to 5 minutes. Add the red-pepper flakes, stir until combined, and cook until the brussels sprouts are crisp-tender, about 2 to 3 minutes. Transfer to a medium bowl.
In the same skillet, heat to medium-high heat and drizzle the remaining 1 tablespoon olive oil. Try to break up any gnocchi that are stuck together before adding them to the pan. Then toss 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.