Oggy and the Cockroaches (1999)

S2E43 Mission To Earth

Oggy and Joey accidentally launch themselves to a distant planet. There, they spot a spaceship on a mission to invade Earth, piloted by aliens disguised as garden gnomes. With the situation now clear, the urgency is undeniable: they must put an end to the gnome aliens' invasion for good and find a way to return home to Earth immediately.