In a blender or food processor, combine the chickpea flour, soy milk, stock, olive oil, garlic, thyme, mustard, salt, and pepper until smooth. Pour into a bowl and let stand for 1 hour.
Preheat the oven to 425�F. Coat a 9-by-13-inch baking pan with cooking spray.
With an electric mixer on high speed, beat the egg whites until stiff peaks form. Add the egg whites to the chickpea batter and pour into the prepared pan. Bake about 15 minutes, until lightly browned around the edges. Let cool for 15 minutes.
Preheat the broiler.
To make the topping, heat the olive oil in a small saucepan. Add the onion and cook about 6 minutes until soft and lightly golden. Add the olives and tomatoes and cook for 1 minute, then remove from the heat.
Spoon the topping evenly over the baked polenta and sprinkle with cheese. Broil for about 1 minute until the top is lightly browned. Sprinkle with parsley and let cool 10 minutes. Cut into squares and serve immediately.
