Preheat oven to 375℉.
Heat a large oven proof saute pan, cast iron would be ideal, lightly coated with 2 tablespoons evoo, over medium heat. Saute onion, carrot and celery, until tender, about 8 minutes.
Add garlic and stir, add ground chicken and cook, stirring for about 4 minutes. Season with salt, pepper, and sage. Stir well.
Sprinkle starch over meat and stir to coat. Add broth, bring to a simmer, and stir in peas if using. Remove pan from heat.
Scatter cauliflower florets over top of dish, drizzle remaining tablespoon evoo, sprinkle thyme, salt and pepper and place in oven until cauliflower is golden and filling is hot about 45 minutes.