1)she's got
a bun in the oven (= she's pregnant)
2)they've got a bun in the oven (= they're an item and she's pregnant)
3)i've got a new application in the oven (=i'm
working on some new software)
4)i've got a new project in the oven (=i'm working on a new project at the office, that is, in
my day job)