Preheat your oven to 425°. Cook a 16oz box of pasta according to the package directions- but be sure to reserve some of the salty pasta water.
Pour a tablespoon of the olive oil into the bottom of a large casserole dish and add the cherry tomatoes in on top. Scatter bits of the onion into the tomatoes, then wedge the feta into the middle of the casserole dish.
Drizzle your tomatoes and feta with the remaining olive oil and the balsamic vinegar, then season to taste with salt and pepper.
Bake your tomatoes and feta for 30-35 minutes or until the tomatoes are bursting and the feta is browned.
Stir the roasted ingredients until a creamy sauce is formed in the casserole dish. Add in some reserved pasta water to adjust the texture of the sauce.
Add the cooked pasta into the sauce, stir, and serve!