Preheat oven to 425 F. Place racks in the top and bottom thirds of the oven.
Leaving the peel intact, cut the butternut squash into 1-inch cubes and wedges. Remove the seeds from the pulp and set aside in a small bowl.
In a large bowl, mix together the harissa, 1 tablespoon of olive oil, and a pinch of salt. Add ½ teaspoon of this mixture to the bowl with the seeds and toss to coat. Add the butternut squash to the bowl with the remaining harissa mixture and toss to coat.
Divide the squash between two sheet pans, some skin side down and some flesh side down and bake for 20 minutes.
After 20 minutes, remove the squash and flip the pieces over, and sprinkle the squash seeds onto the pans. Place the pan that had been on the bottom rack onto the top rack and vice versa. Bake for another 20 minutes, or until squash is tender and cooked through.
Just before serving, whisk together the remaining olive oil and the cider vinegar in a large bowl. Add the salad greens and toss to coat. Slice the avocado.
To serve, place the dressed salad greens on a platter, top with squash, avocado slices, and toasted squash seeds. Season with sea salt and freshly ground black pepper.