Are you driving or will you be arriving by cruise ship?
If you're driving please heed Gypsy Jan's advice and consider postponing your visit until the fire emergencies have abated. They are horrendous on both sides of the border. (FYI, the mandatory evac order for Chula Vista was lifted late last night 10/24)
If you're arriving by cruise ship, Avenida Lopez Mateos is one of the main drags through town and an easy walk from the cruise ship terminal. There really isn't much of interest along this street other than heavily gringoized food and tourist trinkets. There used to be a couple of decent places along the malecon which is also easily reachable by foot from the cruise liner dock. There is a working fish market in Ensenada at the northern end of the malecon where there are any number of places serving delicious mariscos, fish tacos and coctales.
Ensenada has been well covered on this board. A board search should turn up plenty of options for a 1-day visit.
If you are planning to travel in the next few days, you might want to do some research on the latest news reports. Ensenada has a large fire(s) burning in the neighborhoods south of the city proper. Tijuana has fires burning on the eastern boundary and. the last I heard, the Tecate border was closed. The San Ysidro border is open, but inundated by ash from the Portrero fire and the City of Chula Vista is under mandatory evacuation order. The latest news reports estimate that one-in-six San Diegans are evacuated. Qualcomm Stadium in San Diego has 10,000 peole camping there.
This situation is going to go on for some time, so any casual travel plans to Ensenada should take this into consideration.
That being said, please do search this site for on Baja, Ensenada, Mazanillo, Laja and the Guadalupe Valley - there is a wealth of information about great places to dine.