Preheat the oven to 400°F (200°C).
Pat the chicken breasts dry with paper towels.
In a small bowl, mix together the garlic powder, smoked paprika, dried thyme, salt, and black pepper.
Place the chicken breasts on a baking sheet lined with parchment paper or a lightly greased baking dish.
Brush each chicken breast evenly with olive oil.
Sprinkle the spice mixture evenly over both sides of each chicken breast.
Place lemon slices on top of and around the chicken breasts.
Bake in the preheated oven for 25 to 30 minutes, or until the internal temperature reaches 165°F (74°C) and the chicken is cooked through.
Remove from the oven and let the chicken rest for 5 minutes before serving.