Mix in a bowl the chickpea flour, cumin, rosemary, salt and pepper to taste and add the water little by little, stirring vigorously with a whisk to avoid lumps. Cover and let rest for half an hour.
Turn on the oven at 390°F. Cut the pumpkin into small cubes and onion into small pieces.
Put the pumpkin and onion in a pan with a small ladle of water and a drizzle of olive oil. Season with salt, pepper and thyme leaves and simmer over medium heat just until the pumpkin gets soft.
Let the vegetables cool down, then add them to the chickpea batter and mix well.
Lightly grease the bottom and edges of a 12" round baking dish, then pour the frittata batter into it.
Bake the frittata for 25 minutes.
Remove the pan from the oven, lightly brush the surface of the frittata with olive oil, then bake 5 minutes more with grill turned on.
Enjoy your ckickpea frittata, warm or cold.