Whisk the olive oil, lemon zest, lemon juice, honey, and Montreal seasoning together in a bowl. Reserve a couple of tablespoons of the marinade for basting during grilling. This reserved portion is a game-changer, as it enhances the flavor of the chicken.
Place the chicken thighs into a glass dish or zip-top bag. Pour the marinade over the chicken, ensuring each piece is coated evenly. Cover with plastic wrap or seal the bag, and refrigerate for at least an hour (up to overnight) to allow the flavors to soak in.
Heat your grill to medium-high heat. A consistent temperature ensures even cooking and avoids burning the honey in the marinade. Place the chicken thighs on the grill. Cook for 4–6 minutes on the first side, keeping an eye out for nice grill marks. Flip the chicken and baste with the reserved marinade. Cook for another 4–6 minutes, or until the internal temperature reaches 165°F.
Remove the chicken from the grill and transfer it to a plate. Tent it with foil and allow it to rest for about 5 minutes. This step is critical for juicy meat. Sprinkle fresh basil chiffonade over the grilled chicken just before serving.