serried?

If I want to say a certain district has lots of restaurants everywhere, can I say this district "is serried with restaurants"? If not, what other words can / should I use?

"Serried" isn't a commonly used word, so you risk not being understood. I recommend using any of the following words (depending on whether you think having too many restaurants is a positive or a negative feature):

packed
crammed
brimming
saturated
populated
filled
rife
overflowing
bursting
teeming
congested
swarming
glutted

Serried usually refers to things in lines, it is usually found with the word 'ranks', as in 'serried ranks of soldiers' etc.

It wouldn't be applied to restaurants.