Heat 2 tablespoons of the butter in a large nonstick skillet over medium-high; add gnocchi, and cook, stirring occasionally, until browned all over, about 10 minutes. Add garlic and thyme, and cook, stirring often, until fragrant, about 1 minute. Add broth, salt, and pepper; bring to a simmer, and cook until reduced by about half, 4 to 5 minutes. Add peas, parsley, lemon zest, lemon juice, and remaining 2 tablespoons butter; cook, stirring constantly, until butter melts, about 1 minute. Top with Parmesan, and serve immediately.