Preheat the oven to 400°F (200°C).
Prick the whole spaghetti squash several times with a sharp knife to allow steam to escape. Microwave on high for 5 minutes to soften (optional but recommended); if not microwaving, increase oven roasting time as needed.
Carefully cut the squash lengthwise into four pieces and scoop out and discard the seeds.
Brush the cut surfaces of the squash with 1 tsp olive oil and sprinkle with the Italian herb blend. Place the pieces cut-side down on a baking sheet prepared with non-stick spray.
Roast the squash in the oven until the flesh is tender and easily shredded with a fork, about 45 minutes (add time if you skipped the microwave step). Remove and let cool until safe to handle.
While the squash roasts, prepare the vegetables and other ingredients: drain and chop the artichoke hearts; halve the cherry tomatoes and olives; slice the mushrooms; chop the onion and zucchini; thinly slice the green onions; crumble the feta; and mix the broth with the vinegar.
Heat a large non-stick frying pan with high sides over medium-high and add 2 tsp olive oil. Cook the sliced mushrooms until browned and their liquid has evaporated, then transfer them to a plate.
Add the remaining 2 tsp olive oil to the pan, then cook the chopped onion and zucchini about 5 minutes until lightly browned.
Add the minced garlic and 1/2 tsp Italian herb blend to the pan and cook about 2 minutes more.
Pour in the broth and vinegar mixture, reduce heat to medium, and cook about 2 minutes, then return the mushrooms to the pan.
Add the cherry tomatoes, olives, and artichoke hearts and cook about 2 minutes, just until heated through.
Use a fork to shred the cooked spaghetti squash flesh into strands and discard the skins.
Gently fold the shredded squash into the pan with the cooked vegetables, then stir in 3/4 cup crumbled feta until combined.
Taste and season with salt and freshly ground black pepper as needed.
Transfer to a serving dish, sprinkle with remaining feta and sliced green onions, and serve hot.
