Three phase in to UK 3 pin plug

[Marvo]

Why would you need a 3 phase inverter ? you just need to link the the phases together in the appliance .There should be a plate on the oven to tell you the load at 230 volts if it is 14 amps then run a separate supply from the CU then stick in on a 20 amp double pole isolator

Some ovens are suitable for both single and three phase configuration but there may be a 380v or even 230v 3-phase fan (star with centre neutral) in which case there won't be a single phase option.