Soak the cashews in enough boiling water to cover them and allow them to set as you prepare the hamburger. You can also soak the cashews overnight in room temperature water, if this is easier.
Preheat a large nonstick skillet over medium-high heat. Add in the avocado oil. Then toss in the diced white onion and minced garlic. Saute for 30 seconds or until fragrant.
Add the sliced mushrooms (which have been destemmed) and cook them for 2-3 minutes or nicely browned. Sprinkle them with ¼ tsp kosher salt. Stir them for a little longer to distribute the salt.
Add in the ground hamburger meat and cook until the meat is no longer pink. Cook the mixture on high heat to achieve browning and water evaporation. Stir constantly.
Season the meat with 1 tsp salt. You can leave the cooked beef in the pan for now. It will continue to cook as it sits, but that is ok.
Drain the cashews, then place them into a blender along with the water, garlic clove, nutritional yeast, lemon juice, and remaining kosher salt. Blend on high speed for a minute or longer until the mixture is entirely smooth. Taste and adjust, adding more salt or lemon juice.
Drain the palmini. Use a colander/strainer to drain the noodles over a sink. Then place the colander/strainer over a bowl. Divide the noodles into 6 containers.
Divide the meat mixture on top of the noodles. Top with the sauce. Cover with an airtight lid and refrigerate for up to five days.