mmm-yoso!!! is being written by Cathy while Kirk and His Missus are vacationing.
Duke's Old Fashioned Onion Burgers opened less than a month ago at a previous Starbucks location on the North West corner of Baltimore Drive and El Cajon Boulevard. Checking some Instagram photos, it's been owned by this family since at least October, 2021 (when the hood fans were being installed).
Step inside, order, pay and your name is called when ready.
The simple, straightforward menu. Oklahoma-style onion burgers started as a depression-era way to stretch beef. 
Let me say this is a large tray, the serving of French fries is way more than two adults can (should?) eat and the burger and chicken sandwiches on toasted Brioche buns are wonderful. They are also imperfect. 
A single onion burger ($8.95). Fresh ground Angus beef, hand shaped, grilled with plenty of onions.
No, no cheese (which does not cost extra). I did choose lettuce, tomato, mustard and (house made) pickles (excellent!) as toppings (also mayo, ketchup and jalapeños are available as toppings). The plain, crisp edged, smashed burger was unseasoned; when taking a bite with the other ingredients, it was great, but by itself, well, the quality meat was apparent, but I think needed a pinch of salt. (I read some hidden Yelp comments and people were complaining of too much salt during the soft opening, so they went the other way, which is fine.)
The chicken sandwich ($8.95) was quite large and very good. I do think it was in the fryer about ten seconds longer than it should have been; breading was a bit too crisp. Each bite was really tasty.
This photo is deceptive; the serving is really large. The container is deep. The fries ($3.25) are fresh
and are made to order. You are given a choice of ketchup (regular or spicy) or ranch. 
The lemonade is made in house. It is not too sweet and quite nice.
We will be back to try the hand dipped milkshakes; many people were ordering those and sharing an order of fries.
Duke's Old Fashioned Onion Burgers 5020 Baltimore Drive Suite D La Mesa, CA 91942 (619) 439-6177 
that burger looked so delicious!
It looks like the way we make burgers in the fry pan at home…the crisped edges are what does it, Kat. It was very good. Each ingredient fresh, nothing frozen.
How have I not heard of this spot! Onions in the burgers sound perfect!
It’s pretty new, cc; I just saw Duke’s mentioned on Eater.com yesterday. We, of course, were driving by and saw the signage, clueless as we are during certain parts of the year.
I snuck in here today while my son was having a driving lesson at AAA up the road (far far from home – getting mandatory driving lessons for teens is near impossible right now).
I thought that the double was great, with laced crispy edges and all the toppings were quite yummy. Next time I will get a single though!
The owners were there (a couple I believe) and the man was extremely friendly to everyone while still training some new staff. Overall I really like the place and once they get over the start up normal craziness I hope this place makes it!
It’s so good to know you stopped here (instead of the mall), Dereck! It’s good to see a family owned and run business and to be able to try a midwest favorite out here.