Preheat the oven to 400°F / 200°C.
Wash the squash well, then slice into rings about the width of a finger, removing any seeds. Place on a parchment-lined baking sheet, and place in the oven. Set a timer for 10 minutes, at which point you’ll flip the squash. Make the marinade by combining the olive oil, balsamic vinegar, garlic and salt. Set aside.
While the squash is roasting, caramelize the onions. Peel them, slice in half, then into half-moons. Melt the fat of your choice in a large skillet over medium high heat. Add the onion and salt, stir well to coat, then lower the heat to medium-low. Cook for 20-30 minutes, stirring occasionally. Remove from heat and set aside when golden brown.
When the squash is tender, remove from the oven and pour the marinade over top, stirring well to coat. Set aside until ready to serve.
About 10 minutes before serving, make the polenta. Bring water or vegetable broth to a simmer, add the salt and pepper. Slowly pour the polenta in a steady stream into the liquid, whisking constantly to combine. Stir frequently for 5-7 minutes, until smooth and creamy. Remove from heat and add the olive oil, parsley and oregano. Taste and adjust seasoning if desired.
To serve, pour the polenta onto a cutting board, or platter. Top with the marinated squash, caramelized onions, fresh herbs, and feta, if using. Drizzle a touch more olive oil over the top. Say thank you, and enjoy.