Preheat oven to 350 degrees F. Cook unpeeled squash in lightly salted water until crisp tender, about 15 minutes. Drain well. Scoop out most of flesh, leaving 1/4-inch thick shell. Season shell with salt and pepper. Coarsely chop chayote flesh. Set aside.
Heat oil in heavy large skillet over medium high heat. Add onion and salt and saute until tender, about 5 minutes. Add mushrooms and cook until most of liquid evaporates. Add garlic, jalapeno and cumin and saute until fragrant. Add tomatoes and reserved chayote flesh. Stir until most of liquid evaporates. Stir in epazote, bread crumbs and almonds. Season to taste with salt and pepper. Spoon mixture into shells. Sprinkle with cheese. Arrange shells in large baking pan. Pour enough hot water around shells to reach 1/4-inch. Bake until heated through, about 15 minutes.
c.1997, M.S. Milliken & S. Feniger, all rights reserved