Trim and halve brussels sprouts. Zest lemon to make 2 tsp zest.
In large skillet, heat 3 Tbsp olive oil over medium-high. Add brussels sprouts, season with ½ teaspoon salt and a few grinds of pepper, arrange brussels sprouts in an even layer, cut side down. Scatter lemon zest over top and cook, undisturbed, until the brussels sprouts are well browned underneath, 3 to 5 minutes. Add red-pepper flakes, stir and cook until the brussels sprouts are crisp-tender, 2 to 3 minutes. Transfer to medium bowl.
In same skillet, heat remaining 1 Tbsp olive oil over medium-high. Break up any gnocchi that are stuck together, add them to pan. Cook, covered and undisturbed, until golden brown on one side, 2 to 4 minutes. Add butter and honey, season with salt and generous amount of black pepper, and cook, stirring, until the butter is golden, nutty smelling and foaming, 1 to 2 minutes. Stir in brussels sprouts until warmed through. Serve with grated Parmesan.