In a wok or large pan on medium heat, add a drizzle of olive oil, onions and potatoes. Sautee for about 10 minutes, stirring occasionally. Add tomato and carrot and about 1/4 cup water. Cook about 10 more minutes. Add red or green pepper, bouillon, lemon juice, vinegar, Chinese five spice, red chili flakes and salt and cook about 10 more minutes. Mix cornstarch in a little cool water, then add to dish while cooking on stove to thicken sauce, if desired.