In a small bowl, mix together onions, BBQ sauce, Worcestershire, vinegar, brown sugar, pepper, fajita spices, garlic salt, oregano, cayenne, to taste, and garlic. Place ribs in a sealable container and pour the sauce over, turning to coat the meat with the sauce. Refrigerate and marinate at least an hour, or up to 24 hours.
On the SolaReflex 900, use a low black 3 quart pan with a clear glass lid that has a removable knob. You can also use a toaster oven size grill with drip pan inside our optional Clear box oven. Always wear sunglasses when solar cooking. Consider the focal point hot spot the same as an open flame, so use the same common sense and caution. When in direct alignment with the sun, it will reach over 900 degrees F, but normal cooking temps with the diffused hot spot directed on your pan will heat in the 350 to 500 degree F range, depending on sun angle and sky conditions.
Center the cooking container on the support stand, then standing behind your cooking reflector, turn the SolaReflex 900 towards the sun and direct the reflected bright hot spot down to the support stand and center it on right 2/3 of the meat. The hot spot will track right to left as sun moves, so realign the 900 to the same starting position in 25 to 30 minutes, or when the hot spot falls on the left 2/3's of your meat. Reduce heating levels by moving the pot closer to the reflector, which makes a larger hot spot. The smaller the hot spot, the higher the heat level.
Push a probe thermometer through the hole left by the vacant knob, into the bottom of the thickest part of the meat. Normal cooking time on sunny days will be about 45 to 60 minutes. Bright sunny days provide the fastest cooking between 9 am and 2 pm. Partial clouds will slow cooking times and lower temps, so confirm doneness with a meat thermometer.
If the meat starts browning too much on top, open the lid and turn the meat only once to brown the other side.
Note: The ribs can also be cooked on a traditional outdoor grill. Save 1/3 cup marinade for basting, marinate ribs as directed in the recipe. Remove from marinade and grill over medium heat, turning once or twice, until ribs start to pull away from the bone, about 45 minutes. During the last 5 to 10 minutes of cooking, increase heat to medium-high, brush with reserved marinade and grill, turning once, until glazed and crispy.