Step 1: In a large bowl, whisk together the olive oil, red wine vinegar, oregano, garlic powder, salt, and black pepper until well combined.

Step 2: Add the chicken breasts to the bowl and turn to coat them in the marinade. Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or overnight.

Step 3: Preheat your grill or oven to 375°F.

Step 4: Remove the chicken from the marinade and discard any excess marinade.

Step 5: Grill or bake the chicken until it is cooked through, about 20-25 minutes for the grill or 25-30 minutes for the oven.

Step 6: Serve the chicken hot with your favorite side dishes.