In a small pot of boiling water add the peas and cook until tender about 10 minutes, drain. Set aside.
Cook the sausage in a small frying pan adding 3 tablespoons of water, cook until slightly golden, and the water has evaporated (watch that it doesn't burn).
In a medium frying pan add the olive oil, mushrooms, oregano, parsley , salt and the water, cook on medium heat until tender and water has evaporated, stirring occasionally, watch that they don't burn. Then add the drained peas, the Italian sausage (break into smaller pieces if too large) and combine well. Set aside.
FOR THE WHITE SAUCE
In a medium large pot melt the butter over low heat, then add the flour and salt and whisk together until smooth, gradually add the milk, cook and whisk constantly over medium heat until mixture begins to bubble and thicken, remove from heat.
PUTTING IT TOGETHER
In a medium baking pan (I used a 12x10 inch / 30 x 25cm) spread a ladle (using a 1/2 cup ladle) of white sauce on the bottom of the pan (keeps the noodles from sticking) then place the lasagna noodles (or strips) on top (I used 4 for every level, 1 noodle break in half length wise to fit the pan if needed), add 1 1/2 to 2 ladles of white sauce (spread so that it covers the noodles), 1/4 of the sausage/peas mixture spread on top, 1/4 of the chopped mozzarella, and a 1/4 of the grated parmesan cheese continue for 3-4 layers.
Bake for approximately 20-25 minutes, raise the heat and broil for approximately 3 minutes or until the top is golden brown. Let sit for 5-10 minutes before cutting and serving. Enjoy!
**You could always make this into a vegetable lasagna, increase the peas and mushrooms and leave out the Italian sausage.
Depending on your choice of lasagna noodles, some may need to be cooked (boiled) or use oven ready which need no pre-cooking.