Set the oven to 400°F (205°C). Place the chicken breasts on a cutting board and carefully slice approximately three-quarters of the way through the side of each piece to create a pocket. Do not cut completely through the meat.
Season the prepared chicken with the garlic powder, paprika, dried thyme, dried oregano, and salt, distributing the seasonings evenly over the breasts.
Place a slice of mozzarella cheese and several trimmed asparagus spears inside each chicken pocket.
Close the openings as much as possible and fasten them with toothpicks so the cheese and asparagus remain contained while the chicken cooks.
Warm the olive oil in a cast-iron skillet over medium-high heat. When the oil is hot, arrange the stuffed chicken breasts in the skillet.
Sear the chicken for 4–5 minutes on each side, allowing the exterior to develop a lightly browned, golden surface.
After both sides have been seared, place the skillet directly into the preheated oven.
Bake for approximately 15 minutes, or until the chicken is completely cooked and the thickest portion registers an internal temperature of 165°F (74°C).
Remove the skillet from the oven and carefully take the toothpicks out of each chicken breast.
Drizzle the hot stuffed chicken with fresh lemon juice and serve immediately