Preheat oven to 375F.
Lightly grease a 2 quart baking dish with cooking spray and set aside.
Heat olive oil in a large nonstick skillet over medium heat.
Add onions and leeks, and cook for 2 minutes.
Stir in garlic and continue to cook until fragrant, about 30 seconds.
Stir in artichoke hearts and season with thyme; cook for 4 minutes or until heated through, stirring occasionally.
Remove from heat and let cool for 10 minutes.
In a large mixing bowl, combine milk, salt, pepper, and eggs; whisk until thoroughly combined.
Add bread and stir gently to combine.
Stir in artichoke mixture, and let stand for 20 minutes.
Spoon half of bread mixture into previously prepared baking dish.
Sprinkle with half of feta cheese, and top with remaining bread mixture.
Sprinkle remaining feta cheese over top.
Bake for 45 to 50 minutes or until browned and bubbly.
Remove from oven and serve.