Make the marinade Whisk together olive oil, lemon juice, minced garlic, soy sauce, smoked paprika, oregano, garlic powder, salt, pepper, onion powder, and brown sugar until combined. The marinade should taste bold it will mellow slightly as it marinates.
Pound and marinate Place chicken breasts between plastic wrap and pound with a meat mallet to an even half inch to three quarter inch thickness throughout. Place in a zip-top bag, pour marinade over, press out air, and seal. Refrigerate for 30 minutes minimum and up to 2 hours. Do not marinate longer than 3 hours the lemon acid will begin to affect texture.
Preheat grill with two zones Set up two heat zones: one side on high (400-450F) and the other on medium low (300-350F). Preheat for at least 10 minutes. Just before adding chicken, oil the grates with a paper towel dipped in avocado oil held with tongs.
Remove and dry Remove grilled chicken breast from marinade and pat completely dry with paper towels on both sides. Surface moisture slows charring and grill mark development. The flavor has penetrated the liquid on the surface is not needed.
Sear on high heat Place chicken on the high heat zone at a 45 degree angle to the grates. Close the lid. Grill for 3 to 4 minutes without moving. When the chicken releases from the grates naturally and has clear grill marks, rotate 90 degrees for the cross hatch pattern and grill 2 more minutes. Flip and repeat on the other side.
Finish on medium zone Move grilled chicken breast to the medium low heat zone. Close the lid and cook for 4 to 5 more minutes until the internal temperature reads 160 to 162F at the thickest point.
Rest Remove from grill. Tent loosely with foil and rest for 5 full minutes. Carryover cooking will bring the temperature to 165F during resting. Do not cut into it yet.
Serve Slice grilled chicken breast against the grain for the most tender texture. Serve immediately over rice, salad, or with your choice of sides. Spoon any resting juices over the top.