Not advisable, inverters are switch mode devices with feedback, placing them in parallel is not a good idea. At the very least you need to put diodes on the output of each inverter to keep them from feeding back into each other, no telling what this will do to regulation.
Being the two regulators work close to the same operating frequency but have no way to synchronize the harmonics are going to be... weird. It's like throwing an active monkey wrench into both circuits.
There is no circuit simple or complicated to "join the two together".
The output of the inverers is AC, they cannot be paralleled with diodes in the way that DC supplies can be.
The two inverters will not run at exactly the same frequency and in-phase, so just connecting them together will result in a big flash and a bang.
If you could drive both inverters from a common oscillator and ensure that the phasing was correct, it would work.
The easy answer is...
... buy a bigger inverter.
JimB
On edit...
Well I got that wrong didn't I??
As others have pointed out, the OP is powering a 12v device from 230v and so requires a power supply not an inverter.
If you have a 12 volt fridge (or any 12V DC device) that you want to run off 230Volts, you need a step down power supply, not an inverter. The output current of the power supply should be equal or greater than the load current requirement.
Be aware, the nominal voltage in a '12Volt' vehicle is 13 to 15 volts. A power supply intended for automotive DC devices will typically be 13.8 volts.
I do have one concern about the power requirements of your fridge though. 12V @ 1.25 amps sounds awfully low for such a device. Are you sure you read it's label correctly?
By "inverter" I believe he's referring to a 230V AC to 12V DC converter.
You can get a plug pack converter w/ output of 12V/2A (or even 3A or 4A) on ebay for under $10 incl. postage. You may want to consider connecting additional capacitors to the output to help with the motor start current of the fridge though.
If you need more than an amp or 2 just go out and buy a small automotive battery charger witha continuous amp rating higher than what you need.
Stick a big capacitor or set of them inside it (Around 1000 uF per amp continuous output) and you now have a basic multi amp 12 volt DC power supply with the same 11 - 15 voltage working range your vehicle has depending on load.