Slice off the top of the squash to expose the inside. Scoop out the seeds and membranes.
Brush the skin of the squash lightly with the olive oil. Place the squash cut side-down in a baking pan large enough to hold them in a snug, single layer, and pour half an inch of boiling water into the pan.
Bake the squash for about 20 minutes, or until it has softened slightly. Transfer to a plate and let them rest until cool enough to handle. Fill the squash with the cooked filling (recipe follows) and serve.
For the filling:
For the lentils: Bring the lentils, 3 cups of water and 1/2 teaspoon salt to a boil, and simmer on low until lentils are tender, about 10 to 15 minutes. Drain, and set aside.
For the quinoa: Bring 2 cups of water to a boil. Add the quinoa and 1/2 teaspoon salt. Stir, cover and simmer over low heat until the grains are tender and reveal their spiral germ, about 15 minutes.
Warm the olive oil in a wide skillet. Add the onions and sauté until translucent, about 5 minutes. Add the garlic, cumin, kale, corn, peppers, and 2 tablespoons of water. When the kale is wilted, remove the pan from heat and let cool slightly. Stir in the cooked lentils, the cooked quinoa, and the feta cheese. Season with salt and pepper.