Spaghetti with Kale Pesto and Meatballs

In a food processor, pulse together kale, garlic, walnuts, and lemon zest and juice. Add Parmesan and 1/4 cup olive oil and pulse to form a thick paste. Add 1/4 more cup olive oil in a slow steady stream. Season with salt and pepper. Roll sausage into 1" meatballs. In a large skillet, heat remaining 1 tablespoon olive oil over medium-high heat. Add meatballs and cook, stirring, until browned, 10 to 12 minutes. Transfer to a paper towel-lined plate. Pour grease out of skillet and wipe clean with a paper towel. Meanwhile, bring a large pot of salted water to a boil. Cook spaghetti until al dente per package directions. Drain pasta, reserving 1/2 cup pasta water. Add pasta, pesto, and 1/4 cup pasta water to skillet and cook, stirring regularly, 1 to 2 minutes over low heat until pasta is evenly coated. Add meatballs and gently toss to warm. Divide pasta into bowls and top with Parm.