I've never heard of a GPU absolutely needing UEFI.
I know of newer operating systems and SSD's needing such things for the BIOS but not GPU.
There is a thing about GPU software/drivers needing to support UEFI in order to use a UEFI BIOS with it, but that is going forwards with older cards, going backwards you shouldn't have any issue.
And since you are most likely running Windows 7 on it because that's what it ships with, you'll have no issue with newer graphic cards.
The main concern is whether or not the PSU has enough wattage and whether or not it has PCIe power cable support for GPU's that need it.
If you want a simple plug and play GPU that only needs power from the PCIe slot on the motherboard that it plugs into, you can take a look at any lower profile card like the 950 or 1050 and there are certain 1050Ti cards that also don't require extra power from cables.
Most of these cards are low profile and they are single fan coolers on them and small.
But if your PSU has PCIe power connectors, you should count how many pins. At the very least a 6pin cable, but 8pin is better and more than 8pin is nice.
If it does have them, count them and know the limitation as well as know how many watts the PSU can supply, that will help us narrow down the options of GPU for you.