In a large bowl, add the chicken, lemon juice, and olive oil. Toss to coat. Cover and refrigerate for 30 minutes. Preheat the grill. Remove the chicken from the marinade and cut into 1-inch pieces. Discard the used marinade. Arrange the chicken on four wooden skewers alternating with the red onion. Grill the skewers for 5 to 7 minutes on each side or until the chicken is crispy and an internal temperature of 165°F has been reached. Remove the chicken and onion from the skewer and place it into a pita and then top with tomatoes. Repeat this 3 more times with the remaining skewers. Drizzle each pita with 2 tablespoons of Hidden Valley® Original Ranch® Cucumber Dressing. Refrigerate any leftovers promptly in a shallow container. Discard any food left out more than 2 hours (or 1 hour if temperatures are above 90°F).