In a large skillet over medium heat, melt the butter and sauté the onion, celery, and carrots until softened, about 5 minutes.
Sprinkle flour over the vegetables and stir to combine. Gradually add the chicken broth and cream, stirring constantly. Bring to a simmer and cook until the sauce thickens, about 5 minutes.
Add the cooked chicken, frozen peas, thyme, and lemon juice to the skillet. Season with salt and pepper. Stir to combine and cook until everything is heated through, about 3 minutes.
Preheat the oven to 375°F. Transfer the chicken mixture to a 9x13-inch baking dish. Arrange the biscuits on top of the filling.
Bake in the preheated oven until the biscuits are golden brown and the filling is bubbly, about 30-35 minutes.