Zucchini casserole

Ingredients

• 1 to 2 zucchini
• 5 eggs
• 1/2 cup milk
• 1 onion , finely chopped
• 1/2 cup finely chopped ham , about 90 g
• 3 tbsp all-purpose flour
• 2 tsp baking powder
• 1/4 tsp salt
• 1/4 tsp freshly ground black pepper
• 1/8 tsp cayenne pepper
• 2 cups grated extra-old cheddar
• 1/2 cup store-bought dry bread crumbs , or 1 1/2 cups fresh bread crumbs
• 1 1/2 tsp melted butter