In large frypan, place oil and heat to medium-high temperature. Add chicken and cook, turning and sprinkling with salt and pepper, about 5 minutes. Drain oil and discard.
Dissolve bouillon cube in hot water and add to frypan, scraping to loosen pan drippings. Add tomato sauce and mixed vegetables; bring to a boil, reduce temperature, cover and simmer about 25 minutes or until fork can be inserted in chicken with ease.
Stir in half of onion rings. Serve in individual shallow bowls with remaining onions sprinkled on top.