Step 1: Toast the Walnuts
Place the walnuts in a dry skillet over medium heat. Toast for 3–4 minutes until fragrant, stirring constantly. Remove from heat and let them cool completely to lock in the crunch.
Step 2: Prep the Fruit
In a large mixing bowl, toss your diced sweet and tart apples immediately with the fresh lemon juice. This enhances the flavor profile and stops the apples from oxidizing or turning brown.
Step 3: Combine the Salad Base
Add the crisply sliced celery, halved grapes, and the cooled, toasted walnuts directly into the large bowl with your prepped apples.
Step 4: Dress and Toss
Gently fold in the mayonnaise using a rubber spatula until all ingredients are beautifully and evenly coated. Season with a tiny pinch of salt and freshly cracked black pepper.
Step 5: Chill and Serve
Cover the bowl and refrigerate for at least 30 minutes. When ready to serve, arrange a fresh bed of Romaine or Bibb lettuce on a platter, spoon the chilled salad over the top, and enjoy immediately.