In the jar of a high-speed blender, process the spinach, basil, queso fresco, garlic, walnuts, evaporated milk, olive oil, salt, and pepper into a smooth puree. Be sure to scrape down the sides of the blender a couple of times to make sure everything is well blended. Taste and adjust the seasoning if needed. Set the pesto aside or seal and refrigerate until ready to use.
Bring a large pot of water to a boil over high heat. Stir in 1-1/2 tablespoons of kosher salt. Add the pasta and cook according to the package directions.
Turn the burner down to low. Remove 1/3 cup of the pasta water and save. Drain the spaghetti in a colander.
Place the spaghetti back in the pot. Pour the pesto over the pasta and toss to coat. Thin the sauce with a little of the reserved pasta water until you achieve the desired consistency.
Transfer the spaghetti with the pesto verdes to a serving bowl. Sprinkle the parmesan cheese over the top and serve while warm. You can drizzle the dish with a little extra virgin olive oil if desired.