It is generally not safe to eat lasagna that has been cooked with the plastic still on. Plastic materials, especially those not specifically designed for oven use, can melt or release harmful chemicals when exposed to high heat. Ingesting these chemicals can be harmful to your health.
I would strongly advise against consuming the lasagna if the plastic has melted or if there are any signs of plastic contamination. It's better to prioritize your health and discard the lasagna to avoid any potential risks. It's always important to follow proper cooking and food safety guidelines to ensure the safety of your meals.