Preheat the oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish.
In a large skillet over medium-high heat, melt the butter and cook the onions, celery, carrots, and garlic until tender.
Stir in flour, sugar, salt, basil, and pepper, then add the broth and bring to a boil, stirring constantly for 1 minute.
Reduce the heat, add peas, and let it simmer for 5 minutes before mixing in the cooked chicken.
Transfer the mixture to the greased baking dish.
In a separate bowl, combine the baking mix with basil and stir in the milk to create a dough.
Divide the dough into 6-8 balls, flatten them into circles on floured wax paper, and place them over the chicken mixture.
Bake for 30 minutes, then cover with foil and bake for another 10 minutes.
Serve by spooning the chicken mixture over the biscuits.