Cook the pasta in boiling salted water following the package instructions.
Meanwhile, saute the onion in 1 tablespoon of oil, at medium heat and stir occasionally until translucent (for about 10 minutes).
Pour boiling water over the spinach and basil leaves (you can use the same water for the pasta). Strain.
In the blender process onion, garlic, spinach, basil, evaporated milk, white cheese, pecans, olive oil, salt and pepper.
Drain the pasta and mix with the sauce and the green beans. Serve immediately, sprinkled with Parmesan cheese.