In a saucepan, combine tomato sauce, chopped onions, water, brown sugar, lemon juice, Worcestershire sauce, olive oil, mustard, salt and black pepper. Put the saucepan over medium heat, bring the contents to a boil, reduce heat and cook the marinade, uncovered, for about 15 minutes.
Remove pineapples from the jar, drain. Do not pour out the sauce.
Introduce 2 tablespoon. tablespoons of pineapple juice in a saucepan with marinade, mix.
Pour half of the marinade into a separate bowl (reserve), cover and refrigerate.
Pour the remaining marinade from the saucepan into a large zippered plastic bag. Put the shrimps in a bag with the marinade, close the bag, shake and put in the refrigerator for 2-3 hours.
Grease the grill grate with any vegetable oil and turn on the grill to preheat to medium temperature. If using wooden skewers, soak them in water.
Cut pineapple and pepper into pieces with a size of 2.5-3 cm, chop the onion into large pieces.
Remove the shrimps from the marinade bag. On soaked wooden skewers or metal skewers, string shrimp, pineapple pieces, green peppers and onions.
Place the kebabs on the grill rack, cover the grill and fry for about 5 minutes on each side, occasionally brushing with the reserved marinade.