Add olive oil into a pot on medium heat. Add in the diced onions and mushrooms. Cover and allow to cook a few minutes till softened. Next, add in ground meat. Break apart the meat as it cooks. When almost fully cooked, add in the soup mix, flour, and salt. Stir and let cook a minute then mix in the mustard followed by the water. Bring to a boil and allow to thicken. Once thick, remove from heat. 

Preheat oven to 350 degrees Fahrenheit. In an eight-inch or similar sized baking dish, layer the meat sauce followed by the lasagna noodles. Try to add most of the meat to the filling layers, ending off with mostly the creamy sauce as the last layer over the noodles. Cover tightly and bake for 45 minutes. 

Allow to cool a bit before serving – that way, it’ll cut nicely. 

Mix together the mayo, olive oil, vinegar, water, and seasonings. Pour over salad before serving.