Stir together first 7 ingredients. Split biscuits in half; roll each half into a 4-inch circle on a lightly floured surface.
Whisk together egg and 1 tablespoon water in a small bowl until blended.
Spoon ricotta mixture evenly onto each circle, leaving a 1-inch border. Top evenly with tomato. Brush edges lightly with water. Fold dough over filling. Press edges with a fork to seal; prick tops. Brush calzones with egg mixture. Place on lightly greased baking sheets.
Bake at 450° for 6 to 8 minutes or until golden brown. (Do not overbake.) Serve immediately.