PREP the pesto, combine all ingredients except for the water in a food processor and pulse until everything is well combined, but still a bit chunky. Pulse in the water about 1 tbsp at a time, until a spreadable consistency is reached.
PREP the stuffed peppers, preheat the oven to 425°F. Cut the peppers in half lengthwise and remove the ribs and seeds. Place the peppers, cut side down, on a baking sheet and bake for about 4 minutes, flip, and bake another 4 minutes, until slightly softened. Remove from the oven and set aside.
HEAT a large pan over medium-high heat. Sauté the onion, riced cauliflower, and shredded zucchini for about 5 minutes, until slightly softened. Add the ground turkey, season with the salt, pepper, and garlic powder, and continue sautéing for 10-12 minutes, until the turkey is cooked through. Remove from heat and stir in the 1/4 cup of pesto. (Remember to freeze the remaining pesto from the recipe.)
STUFF the peppers with the ground turkey mixture. Cover with foil and return to the oven for 10-12 minutes. Garnish with finely chopped parsley.