Pat dry the chicken breasts with a couple of paper towels.
Season both sides of the chicken breasts with garlic powder, oregano, garlic powder, and pepper.
Grill:
Preheat an outdoor grill to 375F. Once hot, grease the grills with the oil using tongs and some paper towels.
Place the chicken breasts on the hot surface and cook them for about 7 minutes per side until the internal temperature has reached 165F. If the chicken breasts are on the smaller side or you cut them into smaller pieces, the second side might take less time, about 5 minutes.
To grill them indoors, heat a cast-iron skillet or grill pan over medium-high heat. Once hot, grease it. Place the chicken breasts on the pan and cook the first side for 7 minutes. Flip the chicken breasts over and cook for another 7 minutes on the other side until the internal temperature reaches 165F. Cooking time on the second side will vary by the thickness of the chicken breast.
Remove the chicken breasts from the pan onto a board to rest for 5 minutes before slicing.