✓ Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish with olive oil.

✓ In a large skillet, heat the olive oil over medium heat. Add the chopped yellow onion and sauté until translucent, about 5 minutes.

✓ Stir in the diced red bell pepper and continue cooking for another 4-5 minutes until both vegetables are tender but still crisp.

✓ To the skillet, add the peeled and diced sweet potatoes. Cook for 8-10 minutes or until they start to soften slightly. Remove from heat and let it cool for a few minutes before mixing in the baby spinach until wilted.

✓ In a large bowl, beat the eggs with a pinch of salt and pepper. Gradually whisk in the milk until well combined.

✓ Add the sautéed vegetables to the egg mixture, stirring to coat evenly. Fold in the shredded cheddar cheese and crumbled feta if using.

✓ Pour the mixture into the prepared baking dish and smooth out the surface with a spatula.

✓ Bake for 35-40 minutes or until the top is golden brown and the center is set but still slightly jiggly when gently shaken.