At 888 Embarcadero Del Norte, there's a Wingstop that looks like an old Taco Bell without its decorative top, because it was a Taco Bell from 1967 to 1984. It was a Subway from about 1984 to 2020ish.
Taco Bell era
"Remembrance of Isla Vista Eateries Past" says "So have any of you ever wondered why the apartments behind Starbucks are called the “Taco Towers” by longtime locals? That’s because there used to be a Taco Bell where Subway currently is. Look at the architecture of the building front and it is a dead giveaway as to what used to be there."
This Taco Bell opened in about 1967, when Mexican food was still a novelty for a lot of Americans - the Taco Bell menus had pronunciation guides for how to say burrito and taco. Freebirds World Burrito only opened in 1987.
From "The Underground Guide to the College of Your Choice" (1971): "Local hangs include "Borsodi's Coffee House," the "Taco Bell" (where to score) and the "Sun and Earth" (where the freaks hang)."
A post from 2007 says "In late Spring of 1984, the TB was torn down and replaced with a Subway sandwich shop, a (pre-Starbucks) coffee shop, an ice-cream store, and a Chinese restaurant that served dishes such as "Beef Isla Vista" and "Shrimp UCSB"."