Heat oil in a large non-stick frying pan over medium-high heat. Add chicken. Sauté until barely cooked through, about 4 minutes. Sprinkle on half the salt and all the pepper. Remove chicken from pan.
In the same pan, sauté capsicum and zucchini just until tender, 4 minutes. Sprinkle with remaining salt. Add garlic; sauté 30 seconds. Add tomato and oregano. Cook 1 minute. Return chicken to pan. Sprinkle with vinegar; heat through.