Combine lentils and vegetable broth in a medium saucepan. Bring to a boil, then reduce heat and simmer for 20-25 minutes until lentils are tender and liquid is absorbed. Let cool completely.
Heat olive oil in a skillet over medium heat. Sauté onion until soft, about 5 minutes. Add garlic, curry powder, and cumin, cooking for another minute.
In a large bowl, combine cooked lentils, onion mixture, breadcrumbs, parsley, tomato paste, and one beaten egg. Season with salt and pepper. Mix well and refrigerate until completely cool.
Preheat oven to 400°F. Roll out puff pastry sheets and cut each into 2 rectangles. Divide lentil filling among 4 rectangles, placing it in the center and leaving a border.
Brush edges with egg wash, top with remaining pastry rectangles, and seal edges with a fork. Cut small slits in the tops for venting.
Brush tops with egg wash, sprinkle with sesame seeds if using, and place on a parchment-lined baking sheet. Bake for 25-30 minutes until golden brown and puffed.