In a mixing bowl, whisk together 2 Tbsp Cajun seasoning, 1/2 cup Dijon mustard, 1/2 cup honey, and 1 tsp lemon juice until smooth.
Place the chicken breasts in a shallow dish or resealable bag and pour the mustard-honey mixture over them; turn to coat. Marinate in the refrigerator for several hours or up to overnight.
Preheat the oven to 400°F (200°C).
Heat 1 tablespoon oil in an oven-safe skillet over medium-high heat. Sear each chicken breast about 3 minutes per side until golden.
Transfer the skillet to the preheated oven and bake the chicken for 10 minutes, or until an instant-read thermometer registers 165°F (74°C).
Top each chicken breast with a slice of provolone and return to the oven just until the cheese melts, about 1–2 minutes.
Assemble sandwiches by placing the cheesy chicken on pretzel buns and adding desired lettuce and tomato. Serve with extra honey mustard if desired.