Make the chimichurri sauce: In a small food processor or blender, place the parsley, jalapeno, garlic, onion, salt, pepper vinegar, and oil. Pulse to combine, transfer to a Tupperware and set aside.
Preheat the oven to 350 and position a rack in the middle.
Make the pie: line a baking sheet with parchment paper and place the sweet potatoes on top. Transfer to the oven and bake for about 45 minutes, until tender. Remove from the oven and set aside to cool long enough to handle, 10-15 minutes. Remove and discard the skin and place the flesh in either a bowl or a food processor. Add the olive oil, 1.5 tsps of salt, and 1 tsp pepper. Puree or mash until smooth and creamy.
Increase the oven temp to 375.
In a cast-iron skillet or large pan, heat 1/2 tbsp of the butter or olive oil over medium-high heat. Add half the ground beef, 1 tsp of salt, and 1/2 tsp of pepper. Cook, stirring with a spoon until the meat is dark brown and crumbled, 7-10 minutes. Transfer to a baking sheet or plate and repeat with the remaining beef.
Reduce the heat to medium and add the carrots, onion, celery, garlic, and thyme to the same pan. Sweat the vegetables until the onion becomes translucent, 4-5 minutes. Transfer the beef back to the skillet and add the crushed tomatoes and vinegar. Increase the heat to medium-high, stir well, and cook for 10 minutes. Stir in the peas and cook for an additional 5 minutes. Transfer the mixture to a 9x11" casserole dish and spread evenly.
Scoop the pureed sweet potatoes over the top of the filling, use a spatula to create an even layer. Place the casserole in the oven and bake for 30 minutes or until the filling begins to bubble.
Turn the broiler on medium and broil for an additional 4-6 minutes to brown the top. Watch carefully.
Remove the pie from the oven and let it cool for 15 minutes before dividing it evenly into 8 portions. Serve with 2 tbsps chimichurri sauce.