Grill the Chicken: Rub chicken breasts with olive oil, salt, and pepper. Grill on medium heat for 6–7 minutes per side or until cooked through. Let rest and slice.
Prepare the Base: Wash and dry the romaine and greens. Toss them together in a large salad bowl.
Assemble the Salad: Top the greens with sliced apple, blueberries, strawberries, blue cheese crumbles, almonds, and granola. Place sliced grilled chicken on top.
Make the Dressing: In a small bowl, whisk together apple cider vinegar, honey, Dijon mustard, olive oil, salt, and pepper. Drizzle over the salad before serving.