Place walnuts in a food processor and pulse a few times. Add the basil, mint, nutritional yeast, lemon juice, and sea salt and pulse another few times. Leave the food processor on and slowly stream the oil through the opening at the top until all of it is combined. Continue processing to desired consistency (I leave my pesto a bit chunky). Refrigerate until ready to use.
Cook pasta in a large pot according to package instructions (note: I always cook the pasta 3 to 5 minutes less than the package suggests, especially when it comes to gluten-free pasta). Set aside until ready to use.
Heat the avocado oil in a large skillet over medium heat. Add the leek and asparagus and cook, stirring occasionally, until vegetables have softened but are still al dente, about 3 to 5 minutes. Add the peas, lemon zest, and sea salt and continue cooking 1 minute.
Transfer pasta back to the pot you used to cook it, along with the vegetables. Add desired amount of pasta sauce and gently stir everything together (if you're using gluten-free pasta, be extra careful in your stirring or else the pasta will break). Season with sea salt to taste and serve with pumpkin seeds on top.