Ratatouille Galette

Name: Ratatouille Galette
Ingredients: For the Pastry; 1 sprig fresh rosemary; cooking spray; 1.5 cups all-purpose flour; 1/4 teaspoon salt; 8 tablespoons cold unsalted butter, cut into small cubes and chilled; 1/4 cup plain greek yogurt; 2 teaspoons fresh lemon juice; 1/4 cup ice water; For putting it all together; 1/2 cup ricotta cheese; 1/4 cup grated parmesan; 1/4 teaspoon onion powder; 3 garlic cloves, crushed; 1 tablespoon olive oil; fresh black pepper; 1/2 large eggplant, sliced thinly and cut in half moon shapes; 1 yellow squash,sliced thinly; 2 handfuls grape tomatoes, sliced thinly; 1 egg yolk, combined with a dash of water for egg wash