Clifford,
Out of sheer curiosity, what was the name of the food franchise that you were involved with? tell us more if you dare!
In my opinion for what its worth, the oven cleaning business is really only viable if you think of it as a add-on to ones existing cleaning services! most people will only use this service once or twice a year at most, so its going to take sometime & money to drum up enough business, thats unless you want to get involved with the specialist commercial kitchen cleaning companies that affiliate themselves with gas/electrical maintenace contractors to service ducting/extraction fans & HVAC units at major offices and restaurants in city locations!
good luck