Preheat the oven to 400°F.
In a small bowl, combine the Italian seasoning, garlic powder, paprika, salt, and black pepper.
Using a sharp knife, carefully slice into the side of each chicken breast to create a pocket. Do not cut all the way through the chicken.
In a separate bowl, combine 1 tbsp olive oil, the trimmed asparagus, 2 tsp minced garlic, and the red pepper flakes.
Toss until the asparagus is evenly coated.
Drizzle the chicken breasts lightly with olive oil.
Season the chicken evenly with the prepared seasoning mixture.
Rub the remaining 1 tsp minced garlic and the lemon zest over the chicken breasts.
Place 3 asparagus stalks, one-quarter of the chopped sun-dried tomatoes, and 1 slice of mozzarella cheese inside each chicken breast pocket.
Secure the openings with toothpicks, if necessary.
Add 2 tbsp olive oil to an oven-safe skillet over medium-high heat.
Place the stuffed chicken breasts in the skillet.
Sear for approximately 5 minutes per side, or until the chicken is golden brown.
Add the butter to the skillet and allow it to melt.
Pour the lemon juice into the skillet.
Transfer the skillet to the preheated oven.
Bake for 10 to 15 minutes, or until the chicken is fully cooked and reaches an internal temperature of 165°F.
Remove the skillet from the oven.
Allow the chicken to rest for several minutes before serving.
Remove any toothpicks before serving.
Serve warm with the lemon butter sauce from the skillet.