Preheat oven to 350F. Spray an 8-inch by 8-inch cake pan generously with non-stick cooking spray. Scatter the sliced green onions over the bottom of the pan and set aside.

Melt the butter in a skillet over medium low heat. Add the onions and kosher salt, stir or toss to coat. Sweat the onions over the medium low heat, stirring frequently, until they are fragrant and transparent at the edges . Add in the bell pepper and toss again to coat. Sweat the bell pepper for 2 minutes. Stir in the jalapenos and cook for 30 seconds. Scrape the sweated vegetables on top of the sliced green onions.

In a separate bowl, whisk together the eggs, Greek yogurt, milk, oregano, and chili powder until even in colour and no pockets of yogurt remain. Stir in the crumbled feta and/or diced Cheddar cheese. Pour over the vegetables. Stir very slightly just to distribute. Bake for 15 to 18 minutes, or until the edges are puffy, the top is lightly golden, and the omelet is set in the center. Remove the pan from the oven and let rest for at least 5 minutes before slicing into 4 large squares or 9 smaller ones. Serve hot or room temperature with optional toppings as desired, or wrap tightly with plastic wrap to pack for lunches.