The pop star, accompanied by Finalpixx photographer Adnan Ghalib, popped into the Daily Grill in Palm Desert around 10 a.m. Sunday.
"She seemed in a really good mood, laughing with the guy she was with," says the restaurant's manager.
Spears shielded herself behind large, dark sunglasses and "had a champagne mimosa to drink," he said.
She stayed at the restaurant about an hour, as Vegas Confidential's Norm Clarke first reported.
Spears, 26, had been keeping company with Ghalib, 35, before her recent meltdown. The two checked into two hotels over the past couple of weeks, but he was not on hand Friday during her stay in Cedars-Sinai.