1 tablespoon olive oil
1/4 medium red onion, thinly sliced
1 garlic clove, minced
2 cups thinly sliced white button, cremini, or baby bella mushrooms (from about 8 ounces of mushrooms)
1 bunch asparagus (about 10 spears), cut into 1 1/2-inch pieces
1 tablespoon fresh thyme leaves
6 large eggs
1/2 cup feta cheese, cubed
Salt and pepper
Preheat the oven to 400°F. Heat the olive oil in a 10-inch cast iron skillet over medium heat. Add the onions, and cook until fragrant and translucent, about 5 minutes. Add the garlic and mushroom slices, and cook until soft, about 5 minutes. Toss in the asparagus and thyme leaves, cook for another 3 minutes. Season to taste with salt and pepper.
While the veggies are cooking, whisk the eggs, then fold in the cubed feta. When the veggies are ready, pour the egg-cheese mixture over top of the vegetables, making sure the eggs coat the vegetables evenly. Once the edges firm up, transfer the skillet into the preheated oven and bake for 8 to 10 minutes, or until the center is no longer wobbly and the top is golden.