That's a rough crop for winter, even in SoCal. Comparing the size of the leaves to the flower bud opening, they're not doing so great.

How many plants did you have? ...enough to produce enough male/female flowers for timely pollination?

I imagine you'd have a lot less pollinators around this time of year, too.

Peppers and toms are a lot easier out-of-season compared to squash/zukes.

The behavior is very different in Winter. The fruits hang on for days with the flowers still in bloom. I don't think I've seen any male flowers yet. As a result, the fruits are never fertilized and they never size up. I have one zucchini plant going right now. This is a Romanesco hybrid that does really well here in Summer, but I think a trial is in order for a better Winter variety. Still I do harvest a couple of small zucchini a week.

You need to consider day/night length which control flowering and as NC noted, so additional lighting in the proper spectrum might be needed. You also need enough individual plants to assure both male and female flower present at the same time. Finally, you might have better results by hand pollinating the female stigmas with the male flowers. There are also varieties specially bred for greenhouse/tunnel production, very quick setting small bush types, often to harvest no more than 40 days from transplant. You really don't want some old viney variety taking 50-60 days to flower.

Yes, I think with a bit more trialing of different varieties the results might be better. It was a surprise to just have one survive the overnight lows.