Preheat a grill or grill pan over medium-high heat. Season the chicken breasts with garlic powder, onion powder, paprika, salt, and pepper. Drizzle with olive oil and rub the seasonings into the chicken.
Grill the chicken for about 6-7 minutes on each side, or until the internal temperature reaches 165°F. Remove from the grill and let rest for 5 minutes before slicing.
While the chicken is resting, toast the slices of whole grain bread on the grill or in a toaster until golden brown.
In a bowl, combine the chopped romaine lettuce, Caesar dressing, and grated Parmesan cheese. Toss until the lettuce is well coated.
Assemble the sandwiches by placing a generous portion of the Caesar salad mixture on one slice of toasted bread, followed by sliced grilled chicken. Top with additional cherry tomatoes if desired, then place another slice of bread on top.
Optionally, spray the outside of the sandwiches with cooking spray or brush with a little olive oil. Grill the assembled sandwiches for 2-3 minutes on each side until golden brown and crispy.