You're so close to the San Diego Botanic Garden that it would be well worth a visit! Especially since you can see what grows well in your area, paying attention to sunlight, soil, etc. You can either pay for daily tickets or a membership.
San Diego Botanic Garden

On the same street is a very interesting garden called Sunshine Gardens

Your photo shows a lot of shade so it's important to know how many hours of sunlight it receives in both the winter and summer. HTH!

If you were thinking about fruit trees, the fact that you're in San Diego opens up a lot of possibilities that can't be grown in other parts of the country. Particularly exotic tropical fruits many people in America are not that familiar with.

I'd recommend getting a lychee tree. Or visit ONG nursery in the summer and taste the fruits there. Go to a local farmers market and taste some fresh squeezed pomegranate juice. Pomegranates do grow great in Southern California with very little care and produce attractive fiery orange flowers too. Maybe you just don't know the proper technique to easily open and eat a pomegranate. And if you have never tasted the truly fresh squeezed juice, it tastes infinitely better than the pomegranate juice you'll find in the supermarket.

An Oroblanco grapefruit or a Satsuma mandarin tree would also go well in your backyard.

Bananas will grow just fine where you live, and yes, they will taste better off your tree than the ones sold at the supermarket.

If those loquat trees are from seed they probably won't fruit. A Frederick edulis will cover that wall nicely and give fruit too.

You're in a great place to garden and I would start improving the soil and making compost while you decide what you want to grow.