Preheat the oven to 350 degrees F. Place the ground beef and pork sausage in a large sauce pot over medium heat. Brown the meat, breaking into small pieces with a wooden spoon. Once it's mostly cooked, move the ground meat to the side of the pan and add the chopped onions and garlic. Saute for 2-3 minutes, then mix into the ground meat and saute another 2 minutes. Pour the marinara into the pot. Taste, then salt and pepper as needed. Turn off the heat.
Next cut the cauliflower into chunks and place it in the food processor with 1/2 teaspoon salt. Pulse until the cauliflower is broken up into small rice-sized pieces. Dump the cauliflower out onto a paper towel to allow some of the moisture to be drawn out.
Wipe out the food processor before making the cashew "cheese." Add the cashews and all other ingredients. Then turn the food processor on and churn until the mixture is smooth and pasty.
Cut the zucchini lengthwise into thin strips, about 1 millimeter wide. It's easiest to do this with a mandolin slicer. These will be the noodles.
Assemble the lasagna: Spread one-third of the meat sauce over the bottom of a 9x13-inch baking dish. Cover it in a single layer of zucchini noodles. Then spread one-third of the cashew cheese over the zucchini noodles. Sprinkle one-third of the ground cauliflower over the cashew cheese. Repeat two more times, creating three complete layers.
Bake for 30 minutes, until the sides are bubbling and the cauliflower on top starts to toast. Cut and serve warm.
NOTE: It can be easier to spread the cashew cheese on the zucchini noodles before placing them in the baking dish.