Lupita Nyong'o and Joshua Jackson are still going strong ... evident in new PDA-filled photos from their recent trip to Mexico, where they're looking really hot and heavy.

The actor couple couldn't keep their hands off each other down in Puerto Vallarta last week. They certainly look smitten, and for good reason ... these two are an absolute smoke show. Lupita in particular -- who just turned 41, and who's celebrating her bday -- looks amazing.

She seems grateful for the trip -- planting a kiss on Joshua while standing on a lounge chair.

Josh wasn't opposed to the affection -- he wrapped his arms around LN ... even resting his hands on her behind at one point. Yeah, we're looking at a lot of PDA here ... no doubt.

Leave it to these two to make things even hotter in Mexico ... which is already toasty as is.

LN and JJ have been practically inseparable since first being spotted together in October at a concert in Los Angeles. Since the Oscar winner hadn't announced her split from longtime love Selema Masekela ... the outing certainly got tongues waggin'. Now, we know they're an item.

Eventually, the Marvel actress confirmed that she was no longer with Selema -- and proceeded to run errands all over the state of California with her new boo. Since then, they've been seen all over the place ... and they're not trying to hide their love anymore.

Joshua also recently became single.  Remember, his estranged wife, actress Jodie Turner-Smith, filed for divorce after 4 years of marriage. They share one child together, a daughter.

Josh has bounced back and then some ... and ditto for Lupita, obviously.