Preheat the oven to 300 degrees F (150 degrees C).
Bring a large pot of salted water to a boil. Blanch potatoes, zucchini, and bell pepper separately in the boiling water for about 1 minute each. Remove and rinse under cold water, then drain on paper towels.
Whisk eggs, cream, Parmesan cheese, and rosemary together in a bowl until well combined. Season with salt and pepper.
Transfer cooled, blanched vegetables into a round, fluted tart pan. Spread egg mixture evenly over the vegetables. Spoon cottage cheese evenly over the egg mixture.
Bake in the center of the preheated oven until the center is no longer jiggly and the edges are golden brown, about 40 minutes. Remove from the oven.
Mix Greek yogurt, cucumber, radishes, garlic, lemon juice, salt, and pepper for dip together until well combined.