Preheat oven to 400 degrees. Prepare a baking sheet by lining it with parchment paper.
Slice off top end of spaghetti squash and then cut squash in half. Scoop out the seeds.
Place squash halves facing up on the baking sheet and drizzle with 1 tablespoon olive oil and season with salt and pepper.
Turn squash halves face down and roast in the oven for 25 minutes (or until squash is soft when pierced with a fork).
While squash is cooking, in a small pot, heat 1 tablespoon olive oil over medium-low heat.
Add garlic and leeks and saute for 2-3 minutes.
Add feta cheese and lemon juice, stirring continuously until feta is melted.
Add tomato paste and chopped basil and continue stirring until combined.
Set feta sauce aside until spaghetti squash is done.
Once the squash is done, allow it to cool slightly, then carefully flip the squash over and plate them. Then, top each spaghetti squash half with Feta Tomato Sauce.