Preheat your oven to 400 degrees Fahrenheit and line a large baking sheet with parchment paper. Place the pumpkin cubes on the sheet and drizzle with 2 tablespoons of olive oil, then sprinkle with the dried oregano, salt, and pepper. Toss everything together so the pumpkin is evenly coated, then spread the pieces out into a single layer. Roast for 20 to 25 minutes, or until the pumpkin is tender when pierced with a fork and has slightly caramelized edges.
While the pumpkin is in the oven, take a small glass jar or a bowl to make the vinaigrette. Combine the remaining olive oil, apple cider vinegar, and honey. Whisk vigorously or shake the jar until the ingredients are fully combined and the dressing looks smooth. Taste it and add a tiny pinch of salt if you feel it needs more depth.
If your pumpkin seeds are not already toasted, place them in a small dry skillet over medium heat. Stir them constantly for 3 to 5 minutes until they start to turn golden brown and smell fragrant. Immediately remove them from the heat and transfer them to a small plate so they do not continue to cook and burn in the hot pan.
Place the baby spinach or mixed greens into a large, shallow serving bowl or onto a platter. Once the pumpkin has cooled for about 5 minutes, scatter the warm cubes over the greens. Sprinkle the crumbled feta cheese and toasted pumpkin seeds over the top. Just before serving, drizzle the dressing evenly over the salad and toss gently to ensure the leaves are coated without crushing the pumpkin.
