Not nearly as tasty as the new $5 Saturday Market in Thai Town, the vendor area and picnic grounds at Wat Phrathat Doi Suthep USA in Chino Hills have expanded and recently reopened for Sundays from 10am to 3pm.
I would say the foods are hit and miss like those at Wat Thai of Los Angeles, but the place is really nice to hang out for a bit, with plenty of picnic tables and even some music.
More info and photos on my website.