Preheat your grill or grill pan over medium-high heat.
In a small bowl, mix together garlic powder, onion powder, paprika, salt, and pepper. Rub this spice mixture evenly over both sides of the chicken breasts.
Drizzle olive oil on the grill or grill pan to prevent sticking. Place the chicken on the grill and cook for about 6-7 minutes on each side, or until the internal temperature reaches 165°F.
During the last couple of minutes of cooking, place a slice of ham and a slice of Swiss cheese on each chicken breast to melt.
While the chicken is cooking, lightly toast the sandwich rolls on the grill for about 1-2 minutes.
Once the chicken is cooked and the cheese is melted, remove it from the grill and let it rest for a few minutes.
Assemble the sandwiches by spreading Dijon mustard on the bottom half of each roll, adding a layer of baby spinach, and then placing the grilled chicken with ham and cheese on top.
Top with the other half of the roll and serve immediately.