Cut the venison loin into 1-inch cubes and place them in a medium glass bowl.
In a small jar, whisk together the olive oil, balsamic vinegar, oregano, garlic powder, sea salt, and black pepper to create the marinade.
Pour the marinade over the venison, toss to coat thoroughly, and let it marinate for at least 20 minutes at room temperature.
While the meat is marinating, chop the red bell pepper, green bell pepper, and red onion into 1-inch chunks suitable for skewering.
Preheat your grill or a heavy grill pan over medium-high heat until it is very hot.
Thread the marinated venison, peppers, and onions onto skewers, alternating the meat and vegetables evenly.
Grill the skewers for 3 to 4 minutes per side, turning occasionally, until the venison reaches your desired level of doneness and the vegetables are tender.
Remove the kebabs from the grill and let the meat rest for 3 minutes before serving to ensure the juices redistribute.