Step 1: In a large bowl, whisk together lemon juice and mustard. While whisking, slowly pour in the olive oil until the dressing is well combined. Season with salt and pepper.
Step 2: Add spinach, chicken, strawberries, ½ cup pecans, and onion to the bowl with the dressing and toss gently to combine.
Step 3: Serve the salad onto plates and top with the remaining pecans and a generous crumble of feta.