- Heat oven to 375˚. Line a baking sheet with parchment paper and set aside.
- Roll pastry into an 11-by-15-inch rectangle on a lightly floured work surface. Trim sides to make even, transfer to baking sheet and prick all over with a fork. Bake until golden, 10–12 minutes.
- Meanwhile, heat oil in a skillet over medium-low heat. Add onions and cook, stirring occasionally, until golden brown, about 15 minutes. Add swiss chard and cook until wilted. Add garlic and cook until fragrant.
- Lightly score pastry into 4 sections. Top each section with onion mixture, cheese, and an egg.
- Bake until egg whites are set, 12–14 minutes. Sprinkle with herbs and serve.