Add the potatoes and cauliflower to a large pot and fill with enough water to cover them by 1 inch.Cover with a lid and bring to a boil. Remove the lid and reduce the heat to keep it at a low simmer for 15-20 minutes until fork tender.Reserve 1 cup of the potato water and then drain.Use a hand masher to mash the potatoes and cauliflower until nearly smooth. Then add in the butter, ½ teaspoon salt, ½ teaspoon pepper and ¼ cup of the reserved potato water.Mix and add additional potato water as needed and then set aside.
Make the Filling
Heat the avocado oil in a large skillet over medium heat. Add the ground turkey, thyme, ½ teaspoon each salt and pepper and cook for about 5 minutes, stirring and crumbling, until cooked through.
Add the onion to the pan with the turkey and cook for 4-5 minutes until softened. Add the garlic and cook for an additional minute. Stir in the tomato paste, vinegar and vegetables and cook for 2-3 minutes.
Assemble and Bake
To a 3 quart or similar size casserole dish, add the turkey mixture and then top with the mashed potatoes. Bake at 375 °F for 15-20 minutes uncovered until the filling is bubbling up and the potatoes are ever so slightly browned.
Serve.
Notes
LeftoversStore leftovers in an airtight container in the refrigerator for up to 4 days or freeze for up to 3 months. Reheat in the microwave or in the oven at 375 F until heated through.