I have a lasagne recipe that has pumpkin, sausage and collard greens in it. Is there another vegetable that will replace the pumpkin as I do not like pumpkin?
(simple answer) I suggest finding a lasagna recipe without pumpkin in it.
Lasagna is a simple recipe and easily adaptable.
You can add and remove ingredients to your liking as long as you keep the basic structure of the lasagna (pasta/sauce layers).
Make certain that if you add ingredients to the lasagna, that they will be already cooked or can be baked in with the lasagna.
A straightforward replacement would be butternut squash, which can usually be going in either pieces or puree in the frozen section of a grocery store. (In my experience, it is much more common than pumpkin!) It has a very similar flavor profile, texture, and cook time. Acorn squash or a similar "winter squash" could also work, but would involve more prep work -- I've never seen them sold any way but whole.
Since winter squashes are so similar, though, you may dislike the resulting lasagna just as much as if you had used pumpkin. Consider whether the cooking/spices are what you don't like (the classic cinnamon, clove, ginger, etc. in "pumpkin spice" desserts), or the base flavor of the vegetable itself. If it's really the pumpkin, you will probably have a hard time finding a tasty replacement.
Foods which would have a similar texture to pumpkin, either chunked or pureed, are root vegetables such as carrots, parsnips, turnips, or rutabagas. (You will have to adjust the parboiling times to ensure the correct consistency.)
For a puree, mashed peas, e.g., would be an additional option.