Whisk all ingredients together in a small bowl. Set aside.

In a large frying pan, heat oil over high heat.

Add onions and salt; cook for a minute or two, stirring often, until softened slightly.

Add the remaining vegetables and cook for about five minutes, stirring often.

Add half the sauce to the vegetables. Stir and cook for one more minute. Remove from heat and set aside.

Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).

Cut off the tips of each kielbasa, then cut each kielbasa in half, resulting in four smaller pieces.

Place the kielbasa pieces in a roasting pan and top with remaining sauce. Turn to coat each piece fully. Bake, uncovered, for 25 minutes, then broil on high for two minutes.

Cut each roll in half. Spread some of the vegetable mixture inside, then top with a piece of kielbasa and the other half of the roll.