Amanda Bynes -- RELEASED From Mental Facility ... Roaming Sunset Strip

Amanda Bynes has been released from the psychiatric facility where she's been held for more than 2 weeks and was roaming the Sunset Strip Thursday night ... TMZ has learned.

Sources familiar with Amanda's treatment tell TMZ ... she went before a hearing officer at the psychiatric facility Thursday, asking to be released. Amanda has been on her meds and sounds lucid, even though doctor's say she is seriously mentally ill.

The hearing officer felt Amanda was stable enough that she could NOT be held involuntarily, so he ended the 30-day hold that had been granted last week and Amanda walked out the front door.

Amanda walked down Sunset Blvd., searching for a place to stay. She then went to a diner where she ordered a ton of food which she devoured -- fried chicken, salmon, Caesar salad with guacamole, and a house salad with Italian and ranch. She was chitchatting with the waiter and said she was shy because she had a procedure on her face which required a bandage.

Amanda, who paid with a credit card that did not have her name on it, did not seem "with it," according to the waitress. She would carry on a conversation and then when the waitress walked away, Amanda would mumble to herself.

The waitress tells us ... Amanda complained she lost 20 pounds recently and that's why she was so hungry, but didn't want anyone to see her eat because she'd "look like a fat ass."