Heat oven to 400°F. Lightly oil 3-quart Dutch oven or baking dish. On large rimmed baking sheet, toss bread with 1 tablespoon olive oil. Spread in single layer and bake until golden brown, about 10 minutes. Set aside. Reduce oven temp to 350°F. Heat remaining tablespoon oil in large skillet on medium-high. Add sausage and onion and cook, breaking up sausage into small pieces, until sausage is cooked through and onion is translucent, 8 to 10 minutes; stir in sun-dried tomatoes. Remove from heat and toss with spinach. In large bowl, beat together eggs, milk and 1/4 teaspoon each salt and pepper. Add bread and toss to coat, then toss with sausage mixture. Transfer to prepared dish, sprinkle with feta and bake (or cover and refrigerate overnight). Bake until center is just set, 40 to 45 minutes (adding 15 minutes if refrigerated).