Preheat the oven to 400ºF. Toss the broccoli, leeks and lemons together with 2 tablespoons of olive oil. Sprinkle with a pinch of salt and pepper and place on a prepared baking sheet. Roast in the oven until lightly browned and tender, about 25 minutes, tossing halfway through the cooking time. If the leeks are browning too quickly, remove them earlier.
While the vegetables are roasting, prepare the almond parmesan. Combine all of the ingredients in a food processor and process until the "cheese" is similar in texture to grated parmesan. Taste and add more nutritional yeast, salt or garlic powder if needed.
In a large bowl, toss the vegetables with the pasta and drizzle with the remaining tablespoon of olive oil. Stir in the crushed red pepper flakes, and season with salt and pepper to taste. Divide onto plates and serve with the almond parmesan.
Leftover almond parmesan can be refrigerated in an airtight container for several weeks. If you're not a fan of strong lemon flavors, discard the lemon rounds before serving--they'll still infuse the dish with a subtle flavor.