Preheat oven to 375°F (190°C). Generously grease a deep 9-inch pie dish or springform pan with olive oil or butter.

Heat 1 tbsp olive oil in a skillet over medium heat. Sauté chopped onions for 3-4 minutes until translucent. Add minced garlic and cook for 1 minute until fragrant.

Add fresh baby spinach to the skillet and toss for 2 minutes until fully wilted.

Transfer spinach mixture to a fine-mesh strainer or paper towels and squeeze out all excess liquid thoroughly.

In a large bowl, vigorously whisk together eggs, Greek yogurt, whole milk, sea salt, black pepper, and nutmeg until light, bubbly, and aerated (about 60-90 seconds).

Spread squeezed spinach, half of the halved cherry tomatoes, and half of the crumbled feta across the bottom of the greased pan.

Gently pour the egg custard over the fillings. Top with the remaining halved cherry tomatoes so they float near the surface.

Bake for 40 to 45 minutes until the edges are golden brown and the center is set.

Toss whole cherry tomatoes in 1 tsp olive oil with a pinch of salt/pepper. Roast on a small tray alongside quiche during the last 10 minutes of baking until blistered.

Remove quiche from oven. Top immediately with remaining crumbled feta and fresh parsley.

Rest for 10 minutes before slicing into 6 wedges. Serve each slice accompanied by blistered tomatoes and a drizzle of balsamic glaze.