Place 3 Tbsp olive oil, lemon zest and juice, garlic, oregano and pepper in a medium bowl. Add the chicken and toss to coat. Cover and marinate in the fridge for 4 hours, or overnight. Preheat your grill to medium-high. Lightly oil the bars of the grill. Grill the chicken 4 minutes per side, or until cooked through.
Recipe Options: Instead of using 8 boneless, skinless chicken thighs, marinate and grill 4 boneless, skinless, chicken breasts, serving one breast per portion. After grilling and cooling a few minutes, slice the chicken and make Greek-style, handheld sandwiches by stuffing the meat into half pita pockets with tzaziki sauce, feta cheese and diced tomatoes, cucumber and onion.