Preheat a 3.5-quart sauté pan over medium heat. Add olive oil. When oil is hot, add chopped portabella mushrooms and season with salt and pepper. Stirring occasionally, sauté until the mushrooms are lightly brown, about 10-12 minutes. Add minced garlic and sauté just until the garlic is soft and aromatic, about 1 minute. Remove from the heat and cool.
Spray a light coating of cooking spray in the 2.3-quart casserole. Begin layering your lasagna by ladling 1/2 cup of the sauce into the bottom of the casserole and spread evenly. Use 2 of the lasagna noodles to make a layer and cover the sauce. (One noodle will need to be broken to fill smaller areas. Don’t worry about being perfect, the noodles expand.)
Continue to build layers by spreading another 1/2 cup of sauce evenly over the noodles. Sprinkle 1/3 of the shredded vegan mozzarella over the sauce. Then, using a spoon, place 1/3 of the vegan cream cheese in small dollops on the shredded cheese. Use 2 more noodles to create another layer. Spread another 1/2 cup of the sauce evenly over the layer of noodles and then spread 1/2 the mushroom mixture over the sauce. Add another layer of 2 noodles.
Repeat with another 1/2 cup of sauce and the second 1/3 of the shredded and cream cheeses, another layer of noodles and then another 1/2 cup of sauce and the last 1/2 of the mushrooms. Top with another layer of noodles and another 1/2 cup of sauce. Reserve the last 1/3 of the cheeses and the last 1/2 cup of sauce for later.
Place the casserole on the stove at medium heat. When you see vapor escape from the side of the lid (approximately 5 minutes), spin the lid to set the vapor seal and turn the heat to low. Cook on low for 45 minutes.
Remove the lid, spread the last of the sauce and cheeses on top of the lasagna, replace the cover, and cook for a further 10 minutes to melt the cheese. Remove from the heat, let stand for 5–10 minutes and serve.