Combine the ketchup, soy sauce, honey, mustard, brown sugar, garlic and lemon juice in a saucepan over medium heat. Simmer until thickened, about 10 minutes. Let cool.
Cut each chicken thigh into 2 pieces. Peel and core the pineapple; cut into 1-inch chunks. Thread the pieces onto 4 to 6 skewers, alternating between pineapple and chicken. Brush the skewers with olive oil and season with salt and pepper. Remove the garlic cloves from the barbecue sauce and set aside about half of the sauce for serving. Brush the skewers with some of the remaining sauce.
Preheat a grill to medium high. Grill the skewers, turning and basting with the sauce regularly, until cooked through, 10 to 12 minutes. Serve with the reserved sauce.