Step 1: Preheat your oven to 400°F (200°C). Toss the cubed butternut squash with olive oil, cumin, salt, and pepper on a baking sheet. Roast for 25-30 minutes until tender and slightly caramelized.
Step 2: While the squash is roasting, heat a small amount of oil in a skillet over medium heat. Add the minced garlic and sauté for 1 minute, then add the spinach. Cook until just wilted, then remove from heat and squeeze out any excess moisture.
Step 3: Place a tortilla on a flat surface. Sprinkle a layer of Monterey Jack cheese over half of the tortilla. Top with a portion of the roasted squash, wilted spinach, and a bit of goat cheese if using.
Step 4: Add another thin layer of Monterey Jack cheese over the fillings and fold the tortilla in half to create a half-moon shape.
Step 5: Heat a large skillet over medium heat with a tiny bit of butter or oil. Place the quesadilla in the pan and cook for 2-3 minutes per side, or until the tortilla is golden brown and the cheese is completely melted.
Step 6: Remove from the pan, let it sit for a minute, then slice into wedges and serve with your favorite toppings.