Wash and dry romaine lettuce thoroughly, then chop into bite-size pieces. Place in a large bowl, cover, and refrigerate until ready to use.
Season chicken breasts with olive oil, salt, and pepper on both sides. Heat grill pan or outdoor grill to medium-high heat.
Grill chicken for 5-6 minutes per side until internal temperature reaches 165°F. Remove from heat and let rest for 5 minutes before slicing into strips.
Slice strawberries and apple while chicken rests. Divide chilled lettuce between serving bowls.
Assemble salad by spreading sliced fruit evenly over lettuce. Top with craisins, shredded mozzarella, and crushed walnuts.
Add sliced chicken on top and serve immediately with creamy poppyseed dressing (or mix with raspberry vinaigrette) on the side.