Lunch for 1 in SGV
Off the top of my head -- there's Sushi Z on Garfield in Alhambra, right adjacent to San Marino so it's pretty far north. Best sushi in SGV and pretty good all around. Twohey's is also right there -- old fashioned diner with good burgers with chips. I'm very comfortable sitting at the counter solo.
A friend at work really likes Hop Woo on the corner of Garfield and Main (I've not gone), and I also like Pho 79 also on Garfield serves excellent pho, though apparently not the best in town by others' estimation.
Main Street in Old Town Alhambra has the Cuban Bistro, which is probably not great for a singleton and Senor Fish.
These are the place I wish I could eat at lunch time if I were in Alhambra on a weekday afternoon...
Savoy on Valley Blvd for Hainan Chicken and Rice.
Lovebirds for sandwiches.
Cafe Spot for western/HK style dishes
Pepe's for taquitos (is that still around?)
Balé on Valley and Atlantic for bahn mi
Noodle Planet or Noodle World for pad kee mow