Cestrum aurantiacum i believe.

Thanks Ted and Salt, the speed and accuracy of your response was amazing. The plant is definitely Senna (cassia) pendula because Australian websites have spot on photos of the flower. I must claim to being a bit psychic because of my 'weed' reference. It is a declared noxious weed 20 kms away across the NSW border but not here in Queensland. Many thanks, John

figured it out! Yellow Elder or Yellow Trumpetbush (Tecoma stans) ... thanks for looking!

I missed that this was double-posted, or I would have added the id here, too. Ochna does not seem to be a problem plant in SoCal--the name does not appear on the usual problem lists as even a potential issue. Although it reseeds easily, and the birds can disperse the seed, they have not taken hold, possibly due to the lack of regular water/long, dry summers. This is not a widely planted landscape shrub here. Although it reseeds easily in the immediate vicinity around the existing shrubs in my garden, the seedlings are so very slow to get going that they never become a control problem. I have some seedlings that are 2-3 years old, and even with encouragement to grow, are still at or under 6". Once they hit about 20", or if they have access to more fertile soil and adequate irrigation, they tend to grow more quickly.