Season steak with stalk and pepper. Heat 1 tbsp. grape-seed oil in a large skillet over medium-high heat. Add the steak and sear until golden brown on all sides. Transfer the steak to a plate and set aside.
Heat 1/4 cup olive oil in a saucepan over medium-high heat. Add onions and cook for about 4-5 minutes, until onions are soft and translucent. Add garlic and cook for 1 min. Remove from heat and cool mixture.
Place cooled onion mixture in a food processor and add Buitoni Pesto with Basil sauce, baby spinach, walnut halves, and queso fresco. Process to a thick purée. Season with salt and pepper.
In large pot, cook fettuccine per package instructions. Drain, saving 1/4 cup of cooking water.
Transfer green mixture to pot, add cooked fettuccine and 1 tbsp reserved cooking water (or more to reach desired consistency). Gently stir to coat pasta.
Portion pasta on plates and top with steak strips. Garnish with fresh basil.