Arrange bread cubes in a single layer on a baking sheet. Bake at 400°F for 7 minutes or until toasted.
Heat oil in a large skillet over medium-high. Add onion, garlic, and bacon; cook 8 minutes or until bacon is crisp, stirring occasionally. Add spinach; cook 1 to 2 minutes, stirring until wilted. Place spinach mixture in a bowl.
Add milk, stock, eggs, and 1/3 cup cheese to spinach mixture, stirring to combine. Add bread; toss to coat. Divide bread mixture evenly among 4 (7-ounce) ramekins coated with cooking spray. Place ramekins on a baking sheet; top evenly with remaining 1/3 cup cheese. Bake at 400°F for 20 minutes or until browned. Serve immediately.