Although the block of Oakland between Forbes and 5th is littered with "Asian" restaurants, most look dubious at best. Oishii is the sole exception. This clean and cheerful Korean/Japanese eatery serves solid lunch boxes efficiently at a reasonable price.
The bentos and bowls run for about $7. They are generously portioned and contain a good mix of flavors, making for a satisfying quick meal. I am less sure if it'd be worthwhile to get the sushi here. I suspect better quality-to-price deals can be scored elsewhere. I recommend the bibimbap.
Overall, I think the food quality is probably more in the range of 3.5 stars, but I'm rounding up because it is vastly superior to most other Asian fast-food options in Oakland.