In a small bowl, mix olive oil, orange juice, lemon, limes, salt, pepper, and garlic cloves. Keep leftover juiced fruit. Whisk together. Place chicken legs, juiced fruit, and quartered onions in large plastic resealable bags. Pour marinade over the top, tossing to cover completely. Let fruit and chicken marinate for at least two hours; the longer, the better. Remove bags and toss several times over the hours.
Preheat broiler on high. Place rack on the bottom of the oven.
Arrange chicken legs on a broiler pan or any pan with a drip tray. Broil for 25 minutes. Turn the chicken once halfway through to coat the other side.
Warm tortillas wrapped in foil in a separate oven at 300 degrees F or microwave on a plate for 15-20 seconds.
Serve pollo asado with a fiesta of sides: tortillas, beans, guacamole, salsa verde, guacamole, sour cream (and, if you're me, Hint o' Lime Tostitos)