Heat the olive oil in a large skillet over medium heat. Add the onions, garlic, and cumin and cook, stirring occasionally, until the onions are softened, 3 to 4 minutes. Add the beans, squash, tomatoes and their juices, tomato paste and kale; season with salt and pepper. Cook, stirring occasionally, until the kale is wilted, 3 to 5 minutes. Set the vegetable filling aside.
In a 9-by-13-inch baking dish, layer 2 of the tortillas, 1/4 of the vegetable filling and 1/4 cup of the vegan cheese or cashew cheese sauce. Repeat the layers 3 times, ending with the cheese or cheese sauce.
Bake uncovered until the cheese is bubbly and the casserole is hot all the way through, about 20 minutes. Serve with cilantro and vegan sour cream.
Cashew Cheese Sauce:
Yield:Makes about 1 1/2 cups
Soak the cashews in a bowl with cold water for 8 to 12 hours. (Alternatively, "flash soak" them in a heatproof bowl with boiling water for 10 minutes.) Drain then transfer to a food processor or high-powered blender. Add the remaining ingredients and blend until smooth.