In a saucepan over medium heat, add the ketchup, soy sauce, honey, mustard, sugar, garlic, and lemon juice. Bring to a simmer and cook gently until thickened, about 10 minutes. Set aside and cool.
Heat grill pan or outdoor grill. Cut each chicken thigh into 2 pieces. Peel the pineapple and cut it into 1 ½-inch chunks. Alternating between chicken and pineapple, thread the pieces onto the skewers. Brush them with olive oil and season them with salt and pepper. Remove garlic cloves from the barbecue sauce and discard; put about half the sauce into a small bowl for later. Brush skewers with some of the sauce. Cook them on the grill, basting regularly with sauce, until cooked through, about 10 to 15 minutes. Serve with reserved sauce on the side for dipping.