While the celery root and cauliflower are cooking, prepare the filling. Pour olive oil into a 12-inch skillet and set over medium high heat.
Once the oil is hot, add the onion, celery and carrots and saute until they begin to take on color, approximately 4 to 5 minutes.
Add the garlic and stir to combine. Add the lamb, salt and pepper and cook until browned and cooked through, approximately 3-5 minutes.
Drain any excess grease at this point.
Sprinkle the meat with the psyllium husk or cassava flour and toss to coat, continuing to cook for another minute. Add the tomato paste, chicken broth, Worcestershire sauce or coconut aminos, rosemary, thyme, and stir to combine.
Bring to a boil, reduce the heat to low, and simmer slowly 6-8 minutes or until the sauce has thickened.
Add the peas to the meat mixture and spread evenly into an 8 x 11 baking dish.
Top with the garlic mashed veggies and smooth with a spatula.
Place on the middle rack of the oven and bake for 25 minutes or until the top begins to brown. Remove and allow to cool a little before serving as the center will be very hot. Enjoy!