In a large bowl, whisk together seasoning, lemon juice, and oil. Cut chicken into 1" cubes. Add chicken to bowl; stir to evenly coat.
Using a clean cutting board, chop peppers and onion into 1" pieces.
Thread chicken and veggies onto Grill Boss Skewers. Place on grill and cook with lid closed, 12–15 min, rotating often, until lightly charred and chicken is cooked through.