Prep the chicken: Pat chicken dry with paper towels. In a small bowl, mix salt, pepper, smoked paprika, onion powder, and Italian seasoning. Rub the spice mix evenly on both sides of the chicken.
Heat the pan: Place a large skillet over medium-high heat.
Add 1 tablespoon olive oil and 1 tablespoon butter. When the butter foams, swirl to coat.
Cook the chicken: Add chicken in a single layer. Sear 3–4 minutes per side, or until golden and cooked through (internal temperature 165°F/74°C).
Transfer to a plate and tent loosely with foil to rest.
Start the asparagus: Reduce heat to medium. Add remaining 1 tablespoon olive oil to the same pan. Add asparagus and a pinch of salt and pepper.
Toss and cook 3–4 minutes, stirring occasionally, until bright green and slightly tender.
Add the garlic butter: Push asparagus to one side. Add remaining 2 tablespoons butter to the open space. When melted, add minced garlic and a pinch of red pepper flakes if using.
Stir 30 seconds until fragrant, then toss with asparagus to coat.
Brighten it up: Zest half the lemon over the asparagus. Squeeze in the juice of half a lemon. Toss again.
Taste and adjust salt and pepper.
Bring it together: Return chicken and any resting juices to the pan, nestling the pieces among the asparagus. Sprinkle Parmesan over the top. Warm for 1–2 minutes, just until cheese melts and everything is hot.
Finish and serve: Garnish with chopped parsley and extra lemon wedges.
Serve immediately, spooning garlicky butter from the pan over the chicken.