Preheat the oven to 375 degrees. Line a 7-by-11-inch baking dish with parchment.
Heat a large skillet over medium heat. Add 2 tablespoons of vegetable broth or water, the mushrooms, red bell pepper, Simply Organic seasoning, and optional jalapeños. Cook, stirring occasionally, until the vegetables are nearly tender, about 3 minutes.
Add the spinach. Cook until the spinach is cooked down and bright green, about 1 minute. Remove the pan from the heat. Stir in the turkey bacon, and season to taste with salt and pepper.
Spread the spinach mixture evenly on the bottom of the prepared baking dish. Whisk the egg whites, then pour them over the spinach mixture. Scatter the green onions on top.
Bake until the egg whites are set, about 25 minutes. Test by poking a small sharp knife into the middle of the casserole and taking a peek — it should be moist inside, but not liquidy.
Let the casserole sit for about 5 minutes, and then cut into pieces and serve. (The leftovers reheat well in the microwave — just cover and refrigerate.).