Preheat the oven to 425°F. Once preheated, add two rimmed sheet pans to the oven to heat up for 5 minutes.
Prep the carrots. If the carrots are medium-width, bisect lengthwise; if they're fat, cut lengthwise into quarters; if skinny, leave whole. Cut all the carrots into 2-inch pieces on a sharp diagonal. Toss the carrots and onion wedges in 3 tablespoons of olive oil, and season well with salt and pepper.
Transfer the carrots and onions to the heated sheet pans and spread out. Roast for 20 to 25 minutes (20 minutes if carrots are skinny), tossing halfway through.
Add the chopped dates to the pan(s) and roast for 5 to 8 minutes, or until the carrots are tender and slightly caramelized and onions are soft and browned.
Make the pistachio pesto. Add the pistachios to a food processor and blitz until they're in small pieces. Add the parsley, garlic, lemon zest, lemon juice, salt, and black pepper to taste. Blend until a paste forms, scraping down the sides as you go along. With the motor running, stream in the extra virgin olive oil to start to form a sauce. Scrape down the sides again, and stream in more oil as needed until you have a smooth yet thick texture. If the pesto is still not smooth enough but you don't want to add more oil, add a spoon of water at a time until the sauce comes together into a creamy, spoonable consistency. Taste for seasonings, adding more salt, lemon, or garlic as needed. Make the seed sprinkle. Heat a small or medium frying pan over medium heat. After a minute or two, add the olive oil and pepitas, red pepper flakes, cumin, paprika, cayenne, and 1/4 teaspoon kosher salt. Stir almost continuously until golden and seeds are popping, 2 to 2 1/2 minutes. Transfer to a plate and spread out with a spoon, ensuring that the spices evenly coat the pepitas. Allow to cool. Assemble the dish. Spoon some of the pesto on a platter. Add the roasted carrots, onions, and dates on top. Scatter some seed sprinkle on top and garnish with chopped parsley.