Heat the oil in a wok or large pot over medium-high heat. Cut each chicken schnitzel into approx 2cm strips and add to the hot oil, cooking 6 minutes until slightly browned. Transfer the chicken to a plate and set aside.
In the wok add a splash more oil and pop in the onion, garlic and ginger and cook 2 to 3 minutes stirring regularly. Add in the mushrooms, tomatoes, garam masala, ground fennel seed, cumin, coriander, turmeric, and cinnamon. Cook for a couple minutes, stirring frequently.
Return the chicken to the wok, along with the juices from the plate. Bring to a boil over high heat. Reduce heat to medium-low and simmer, covered, for 10-15 minutes, stirring occasionally and testing the chicken is tender.