Heat oven to 350°F. Spray 11x7-inch (2-quart) glass baking dish with cooking spray.
In large bowl, beat eggs with wire whisk. Add pesto and milk; beat until blended. Separate dough into 8 biscuits; cut each into quarters. Gently stir biscuit pieces into egg mixture to coat evenly. Fold in cheese and tomatoes. Spoon mixture into baking dish, arranging biscuit pieces in single layer.
Bake 23 to 25 minutes or until golden brown. Sprinkle with onions. Cut into squares.