1. Cook frozen vegetables according to package directions until tender crisp. Drain very well, blotting any excess liquid. Place in a greased 6-cup (1.5L) baking dish. Combine vegetables and chicken. Reserve while making sauce.
2. In a saucepan, melt butter over medium heat. Add onion and cook 3 to 4 minutes until softened. Stir in flour and cook, stirring for 3 minutes, until light golden. Gradually whisk in stock. Bring to a gentle boil and cook for 3 to 4 minutes until sauce thickens. Add thyme, salt and pepper. Pour over vegetables and chicken. Stir gently to combine.

Topping:

1. 
   For the topping, in a bowl combine flour, cornmeal, baking powder, salt and cheese. In a separate bowl, combine oil, milk and egg. Add to flour mixture and stir to combine. Spoon topping over chicken and vegetables. Place dish on a baking sheet.
2. Bake in a preheated 425ºF (210ºC) oven for 25 minutes. Until topping is golden and bottom is bubbling.

Make Ahead:

Sauce can be cooked ahead of time, covered and refrigerated for one day.