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 beef, season with the salt, pepper, and garlic powder, and continue sautéing for 10-12 minutes, until the beef 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 beef mixture. Cover with foil and return to the oven for 10-12 minutes. Garnish with finely chopped parsley.
Notes
Note: This makes about 1 cup of pesto. Reserve 1/4 cup for this recipe and freeze the rest. An easy way to do this is to spoon by the tablespoonful into an ice cube tray, freeze, then pop out and store in a ziploc bag.I cube = 1 tbsp of pesto.