Pickle the grapes: Place the halved grapes in a small bowl with red wine vinegar and set aside for 10-15 minutes.
Prepare the pesto: Using a small food processor or mortar and pestle, pulse together the pine nuts, parmesan, garlic, basil, olive oil, salt, and pepper until smooth. Season with salt and pepper to taste.
Sear the chicken: Pat chicken dry with paper towel. Season both sides generously with salt and pepper. Heat 1 tablespoon olive oil in a skillet over medium-high heat. Add the chicken and cook for 4-6 minutes per side, until golden brown and cooked through. Transfer to a cutting board and let cool slightly before cutting into bite-sized pieces.
Cook the pasta: In a large pot of boiling salted water, cook the pasta until al dente (according to package instructions). Reserve 125 ml of the cooking water. Drain and rinse under cold water to stop the cooking process. Transfer to a large bowl.
Combine: Add the pesto to the bowl with the pasta and toss until well combined. If needed, add a little pasta cooking water (1 tablespoon at a time) to thin the pesto.
Add remaining ingredients: Drain the grapes and add them along with the chopped chicken and spinach (or arugula) to the pasta. Toss to incorporate.
Serve: Garnish with toasted pine nuts and freshly grated parmesan cheese. Serve and enjoy!
For a relaxing atmosphere in the kitchen I recommend my personal Elle Republic: Chilled Out Kitchen Tunes Playlist on Spotify.