Left Lasagna out all night - Safe to eat

Yes.

LINK

When in Doubt, Throw it Out!

You cannot always see or smell bacterial contamination. Mold that appears to be growing only on the surface may grow invisible roots into softer foods. Do not rely on a visual inspection or "smell test" to tell you whether or not a food is safe. It's not worth the risk - food poisoning can be much, much worse than an upset stomach.

The Danger Zone

Potentially hazardous food that stays in the temperature "danger zone", 40-140 °F (4-60 °C), for more than 2 hours should be discarded.*
Potentially hazardous foods are those foods that spoil most easily, such as unshelled eggs, raw meats, fish, shell fish, dairy products, almost all cooked foods.
This time is cumulative, so it includes time bringing the food home from the grocery store, time before cooking, time after cooking, and so on. The reason is that while cooking may destroy bacteria or other pathogens, it doesn't always destroy the toxins that they have produced.
So in general, regarding perishable foods like meat, most dairy, unshelled eggs and shell eggs (in the US), cooked casseroles, and so on: if the food (or its perishable components) have been at room temperature for more than two hours, you should discard that food.
To avoid the danger zone, keep cooked food hot until ready to eat, then refrigerate immediately. Separate large items into smaller containers to help them to cool more quickly. If you’re defrosting something, do it in the fridge or under cold running water.
If you can be certain that the food was not in the danger zone, then yes, it is safe. For example, if you left a large chunk of frozen meat out and it is still frozen solid when you come back to it, it was not in the danger zone.
Why does cooking not completely "reset the clock"?

Some bacteria leave behind harmful protein toxins that cannot be "killed" (denatured) by cooking. Cooking food is only effective against live organisms, not their toxic waste products. Spoiled food cannot be cooked back to safety and must be discarded.
Cooking is pasteurization, not sterilization. Pasteurization means killing most microbes, so as to render the food safe for human consumption. Sterilization methods (e.g. pressure-canning and irradiation) are the only safe methods for longer-term room-temperature storage. Otherwise, the danger zone rules always apply.
Even sterilized food can only remain sterile under an airtight seal, e.g. when properly canned or vacuum-sealed. Once it is opened, it is no longer sterile. Air contains countless bacteria and molds, and their spores, which will readily re-colonize any suitable environment they encounter. Cooked food tends to be an ideal medium for growth.

I would 100% eat it. It's fine.

t00f's only saying that it cannot be affirmatively claimed safe to eat. Each person has a different acceptable risk. I've eaten food that's been at room temp for three hours (say, party leftovers) but never overnight. But I'm more risk averse with expiration dates, etc, so YMMV.

Toss it. Not safe.

I wouldn't risk it, but you're the one that would have to deal with spewing from both ends.

It's always safe until it isn't.

Officially it is unsafe to eat. IMO it's worth the risk and you'll probably be o.k. That's coming from someone who's had food poisoning more than once though so consider the source. I'm assuming this is a homemade lasagna and not Stouffer's, correct?

im always of the "eat it" camp. But then again I'm disgusting with no regard to my health.