Heat oven to 350ºF. Line a sheet pan with foil or parchment paper.
Halve the spaghetti squash crosswise and use a spoon to scrape out the seeds and stringy yellow strands, then discard. (See notes in post for how to cut open a spaghetti squash.)
Drizzle olive oil over the flesh.
Season the flesh with a pinch of salt & pepper then fill the squash with garlic, sun-dried tomatoes and feta cheese.
Season with Italian seasoning and some more olive oil.
Bake until the flesh can be easily pierced with a fork, 45 to 55 minutes.
Remove the pan from the oven and let cool for 10 minutes.
Using a fork, gently pull the squash flesh from the sides and mix with the sun-dried tomatoes and feta; the squash will separate into spaghetti-like strands.
Add fresh basil, Pecorino Romano, and balsamic vinegar. Toss well and serve immediately,