Heat the vegetable oil in a large frying pan and cook tortillas, in batches, until golden and crisp. Drain on paper towels cut into strips and set aside.
In separate medium sized saucepan, heat olive oil and cook garlic on gentle heat for 1 minute, stirring frequently.
Add tomatoes, onion, chillies and oregano and cook for 5 minutes, stirring occasionally. Add the water, Knorr Chicken Stock Pot and tomato paste.
Bring to the boil then simmer uncovered, stirring occasionally for 20 minutes.
Process mixture in food processor or blender, in batches, until smooth. Return soup to saucepot.
Stir in chicken, corn and baby marrow. Bring to the boil over high heat, stirring occasionally. Reduce heat to medium, then add tortilla strips. Simmer, stirring occasionally, 3 minutes. Stir in lime juice. Garnish, if desired, with chopped fresh coriander, diced avocado, sour cream, lime wedges and additional fried tortilla strips.