Kellan Lutz -- Celebrates Bday with 1 Hot Chick on an Elephant ... and a Bunch of Dudes

Screw making it rain on strippers for his 29th birthday ... Kellan Lutz just wanted to let loose in Thailand with his bros.

The "Twilight" star celebrated the festivities on Nikki Beach Phuket in what looked like a cabana ... and a hot model delivered his birthday cake atop a baby elephant.

Then the group of bros all posed for pics wearing shirts that said, "A celebration of life" -- while Kellan's name was lit up on some kinda outdoor fire display.