Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Halve the baby potatoes and trim the tough, woody ends off the asparagus spears.
Place the chicken breast, halved potatoes, and trimmed asparagus onto the prepared sheet pan.
Drizzle the olive oil over the chicken and vegetables, then sprinkle evenly with dried rosemary, garlic powder, sea salt, and black pepper.
Slice the lemon half into thin rounds and arrange them over the chicken and asparagus to infuse them with bright citrus notes.
Toss the vegetables gently to ensure they are well-coated in the oil and spices, then spread them out in a single layer.
Roast in the center of the oven for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the potatoes are fork-tender.
Remove from the oven and let the chicken rest for 5 minutes before slicing to keep it juicy.