Add ketchup, soy sauce, honey, mustard, lemon juice, brown sugar and garlic to a small pan and cook for 10 minutes. Remove from heat and allow to cool.
Cut chicken, peppers and onion into 1 1/2 in cubes.
Peel and core pineapple and cut into 1 1/2" cubes.
Place Pineapple, chicken and vegetables onto skewers alternating pieces.
Transfer 1/2 of sauce to another dish to use when serving.
Brush skewers with oil then with sauce and place on heated grill.
Baste skewers every 3-5 minutes while cooking. Cook for about 15 minutes.